Maximum allowable slope, 29 CFR 1926 Subpart P Appendix B
Length times width times depth describes a hole with vertical sides, and past five feet in anything that is not rock, OSHA does not let you leave one open. The sides get shored or they get laid back, and Appendix B says how far: three quarters of a foot of run per foot of depth in Type A, one to one in Type B, one and a half to one in Type C. Fifty feet of a 4 ft wide, 8 ft deep trench is 59 cubic yards as a box and 308 sloped to the Type C maximum.
Trench volume at the permitted slope, and what the box misses
ft
ft
ft
%
The soil type defaults to C, because 1926.652(b)(1) is explicit that an employer who does not classify the soil slopes to the Type C figure. Classification is done on site by a competent person, not by a dropdown.
Specification summary
Generated from on .
Reopen that address to reproduce these figures exactly.
Entered
Result
Section across the trench, box against laid-back slope
Published excavation and grading prices, and how old they are
Not this site's numbers. Lawn Love, how much does land grading cost, Written by Sinziana Spiridon, published 27 December 2025 and read here on 2026-09-09.
As published by Lawn Love, how much does land grading cost, mixed, and the unit is on every row
Item
Low
High
Unit
Excavation, cut and fill
$60
$200
per cu yd
Fill dirt, material only
$6
$17
per cu yd
Grading, with operator
$40
$180
per hour
Fine grading
$0.08
$1
per sq ft
Rough grading
$1
$2
per sq ft
Topographic survey
$500
$1,200
total
Grading permit
$150
$485
total
Excavator hire, no operator
$240
$470
per day
Backhoe hire, no operator
$185
$500
per day
Skid steer hire, no operator
$240
$340
per day
Dump truck hire, no operator
$250
$550
per day
Source: Lawn Love, how much does land grading cost, published 27 December 2025, read 2026-09-09. The rows are on four different bases and cannot be added together. The per cubic yard excavation figure is a service rate that already includes the machine and the operator; the hire rows are for DIY without an operator, which is why they look cheap beside it. The permit figure is the publisher's range across counties and it notes the trigger is disturbing over 5,000 square feet, which varies by jurisdiction and is not something a national range can settle for your site.
Fifty feet of trench, 4 ft wide at the bottom, 8 ft deep, in unclassified soil, which is Type C.
The box. 50 × 4 × 8 = 1,600 cu ft = 59.3 cu yd.
The lay-back. 1.5 × 8 = 12 ft each side, so the opening is 74 ft × 28 ft.
The real volume. The prismatoid rule gives 308.1 cu yd.
The multiple. 308.1 ÷ 59.3 = 5.20 times the box.
The spoil. At a 25% bulking allowance, 385.2 cu yd to handle.
The egress. 8 ft is past 4 ft, so a ladder within 25 ft of lateral travel: 1 ladder for a 50 ft run.
At the quoted 60 to 200 dollars per cubic yard, the box says 3,556 to 11,852 and the sloped section says 18,489 to 61,630. That is the same trench, on the same site, in the same soil. One of the two numbers is the shape you are allowed to dig, and it is not the one every calculator gives you.
The formula
The taper is linear, so the prismatoid rule is exact and a top-and-bottom average is not:
V = D/6 × (Ab + 4Am + At) At = (L + 2rD)(W + 2rD)
L, W, D
trench length and width at the BOTTOM, and depth, in ft
r
maximum allowable slope as run per 1 ft of rise. 0.75, 1 or 1.5
Ab
bottom area, L × W
Am
area at half depth, (L + rD)(W + rD)
At
area at the surface
r = 0
stable rock, where the prismatoid collapses back to the box
Averaging the top and bottom areas and multiplying by the depth overstates the volume, because the taper makes the mid-depth area smaller than the average of the two ends. The prismatoid rule handles that exactly, which is why it is used here rather than the easier approximation.
Why this page starts with the shape rather than the volume
There is nothing to get wrong about length times width times depth, and every excavation calculator on the internet does it correctly. That is the problem. The arithmetic is right and the shape is wrong.
A trench with vertical sides is a shape OSHA permits only in stable rock, or under five feet with a competent person's examination. Everything else gets sloped, shored or shielded, and on a small job the answer is almost always sloped, because it needs no hire, no shield and no design.
Once the sides are laid back, the volume stops being a box. In Type C soil, which is the code's own default when nobody classifies the ground, a 4 ft wide 8 ft deep trench opens out to 28 ft at the surface and the volume goes up more than fivefold.
So the number a homeowner uses to book a skip, hire a machine or budget a job is not off by a percentage. It is off by a multiple, and the multiple is set by a soil classification made on site by a person, which no calculator can perform.
Maximum allowable slope by soil type, Figure B-1
Soil
Maximum allowable slope
From horizontal
Top width of a 4 ft wide, 8 ft deep trench
50 ft of that trench
What the standard says it is
Stable rock
vertical
vertical
4 ft
59 cu yd
1926.652(a)(1)(i). Vertical sides are permitted, and stable rock is defined as natural solid mineral matter that can be excavated with vertical sides and remain intact while exposed.
Type A
3/4:1
53°
16 ft
169 cu yd
Cohesive soil at 1.5 tsf unconfined compressive strength or greater. NOT Type A if it is fissured, subject to vibration from traffic or pile driving, or previously disturbed.
Type A, short term
1/2:1
63°
12 ft
130 cu yd
The exception under B-1.1. Open 24 hours or less AND 12 feet or less deep, both conditions, in Type A soil.
Type B
1:1
45°
20 ft
213 cu yd
Cohesive soil between 0.5 and 1.5 tsf, granular cohesionless soils including angular gravel, silt, silt loam and sandy loam, and previously disturbed soils that are not Type C.
Type C
1 1/2:1
34°
28 ft
308 cu yd
Cohesive soil at 0.5 tsf or less, granular soils including gravel, sand and loamy sand, submerged soil or soil from which water is freely seeping. Also the DEFAULT under 1926.652(b)(1) when no classification is done.
Read 2026-09-09. Ratios and the final column quoted or summarised from 29 CFR 1926 Subpart P. The two volume columns are this page working the ratio through a worked trench, not figures from the standard.
The hole is not a box, and the multiplier is the soil type
Length times width times depth describes an excavation with vertical sides. At five feet, in anything that is not rock, that is not a shape you are permitted to leave open:
Each employee in an excavation shall be protected from cave-ins by an adequate protective system designed in accordance with paragraph (b) or (c) of this section except when: (i) Excavations are made entirely in stable rock; or (ii) Excavations are less than 5 feet (1.52m) in depth and examination of the ground by a competent person provides no indication of a potential cave-in.
So the sides get supported, or they get laid back. Laying them back needs no shoring, no shield and no hire, which is why most small jobs do it, and Appendix B sets how far:
29 CFR 1926 Subpart P Appendix B, Figure B-1, simple slope, excavations 20 ft or less in depth
Soil
Maximum allowable slope
From horizontal
Top width of a 4 ft wide, 8 ft deep trench
50 ft of that trench
What the standard says it is
Stable rock
vertical
vertical
4 ft
59 cu yd
1926.652(a)(1)(i). Vertical sides are permitted, and stable rock is defined as natural solid mineral matter that can be excavated with vertical sides and remain intact while exposed.
Type A
3/4:1
53°
16 ft
169 cu yd
Cohesive soil at 1.5 tsf unconfined compressive strength or greater. NOT Type A if it is fissured, subject to vibration from traffic or pile driving, or previously disturbed.
Type A, short term
1/2:1
63°
12 ft
130 cu yd
The exception under B-1.1. Open 24 hours or less AND 12 feet or less deep, both conditions, in Type A soil.
Type B
1:1
45°
20 ft
213 cu yd
Cohesive soil between 0.5 and 1.5 tsf, granular cohesionless soils including angular gravel, silt, silt loam and sandy loam, and previously disturbed soils that are not Type C.
Type C
1 1/2:1
34°
28 ft
308 cu yd
Cohesive soil at 0.5 tsf or less, granular soils including gravel, sand and loamy sand, submerged soil or soil from which water is freely seeping. Also the DEFAULT under 1926.652(b)(1) when no classification is done.
Read the last column against the box. Fifty feet of a 4 ft wide, 8 ft deep trench is 59 cubic yards if you multiply the three dimensions together. Sloped to the Type C maximum it is 308, which is 5.2 times as much soil to dig, to move and to put back.
That is not a refinement. It is the difference between a day and a week, and between one skip and five.
The ratios are run over rise, which is the opposite of how roof pitch is written and catches people out constantly:
Maximum allowable slope means the steepest incline of an excavation face that is acceptable for the most favorable site conditions as protection against cave-ins, and is expressed as the ratio of horizontal distance to vertical rise (H:V).
The default is Type C, and it is the code that says so
Soil classification is done by a competent person under Appendix A, with a visual and a manual test. Plenty of jobs do not do it, and the standard anticipates that. It offers four options for designing a slope, and the first one is the option for not classifying anything:
Excavations shall be sloped at an angle not steeper than one and one-half horizontal to one vertical (34 degrees measured from the horizontal), unless the employer uses one of the other options listed below.
One and one half horizontal to one vertical is the Type C figure, the flattest in the table. So the price of not classifying the soil is that you dig the widest hole in the standard, and the code is explicit that this is the trade.
Which is why this calculator defaults to Type C. Every excavation calculator that quietly assumes something steeper has assumed the most favourable soil conditions in the standard on your behalf, on a page that has never seen your ground.
And even a correct classification is a ceiling rather than a target. Two things flatten it further:
The actual slope shall be less steep than the maximum allowable slope, when there are signs of distress. If that situation occurs, the slope shall be cut back to an actual slope which is at least 1/2 horizontal to one vertical (1/2 H:1V) less steep than the maximum allowable slope.
When surcharge loads from stored material or equipment, operating equipment, or traffic are present, a competent person shall determine the degree to which the actual slope must be reduced below the maximum allowable slope, and shall assure that such reduction is achieved.
A spoil heap beside the trench is a surcharge load. So is the mini digger that put it there, and so is the road if the trench runs beside one.
Width at the bottom, not at the top
The width input on this page is the width at the BOTTOM of the trench, and getting that the wrong way round is the most likely way to misuse it.
The bottom width is a real design dimension: it is set by what has to fit in the trench and by what the person in it needs to work. A pipe bedded in gravel with room to joint it, a footing with formwork, a bucket that comes in a fixed width. Those decide the bottom.
The top width is an output. It is the bottom plus twice the lay-back, and it is the number that tells you whether the excavation fits on the site at all. A 4 ft trench 8 ft deep in Type C soil opens to 28 ft, and on a 30 ft wide garden with a fence on both sides that is the end of the sloping option before the volume matters.
When the top width does not fit, the answer is a shield or shoring rather than a flatter slope. That is what a trench box is for, and it is why they are hired on jobs that look far too small to need one. This page calculates the sloped option because it is the one with a volume; it is not a recommendation that sloping is the right choice on your site.
Grading is a different question, and it is priced differently
A good share of the people who look for an excavation calculator are actually grading: reshaping the surface of a yard rather than digging a hole in it. The two are not the same calculation and they are not sold the same way.
Grading is priced by area. The source quoted below gives a fine grading range and a rough grading range, both per square foot, and an hourly rate with the machine and operator included. There is no depth in any of those, because the depth of a cut and fill job varies across the site and the contractor is pricing the job rather than the volume.
Excavation is priced by volume, per cubic yard, and that is the row this calculator multiplies.
The connection between them is cut and fill: material scraped off the high side gets moved to the low side, and only the difference is bought in or taken away. That balance is what a topographic survey is for, and it is not something a calculator with one depth input can do. If your job is a slope rather than a trench, the per square foot rows in the price table are the ones to look at, and the volume above is not your answer.
The heap is bigger than the hole, and nobody will tell you by how much
Soil in the ground is compacted by everything that has happened to it since it got there. Dig it and you break that structure, air gets in between the clods, and the same material occupies more space. Backfill it and it will not go back in, and you either have a mound or a surplus to take away.
The percentage is not published anywhere this site could find, for the same reason no government publication tabulates the weight of a heap of gravel: it is a property of a specific soil at a specific moisture on a specific day, not a property of a product. Contractors' handbooks print swell tables, and the ones traceable from here sat behind a paywall or on a page with no author and no date.
So it is an input here. It defaults to a round 25%, that figure is this page's own, and the page says so rather than crediting it to somebody. If you have a geotechnical report for the site, it will have a real number in it and you should use that instead.
What the arithmetic does tell you is the shape of the problem. The sloped volume is already several times the box, and the swell is a further multiple on top of it. A trench that looks like a two-yard skip on paper is routinely three loads by the time it is out of the ground.
Where the spoil goes, and the ladder you have to be able to reach
Two more rules in the same subpart change the shape of a small site, and neither is about volume:
Protection shall be provided by placing and keeping such materials or equipment at least 2 feet (.61 m) from the edge of excavations, or by the use of retaining devices that are sufficient to prevent materials or equipment from falling or rolling into excavations, or by a combination of both if necessary.
The heap has to start at least 2 feet back from the edge. On a garden job with a fence line, that is often the constraint that decides whether the soil stays on site at all, and the heap is bigger than the hole it came out of because dug soil bulks.
A stairway, ladder, ramp or other safe means of egress shall be located in trench excavations that are 4 feet (1.22 m) or more in depth so as to require no more than 25 feet (7.62 m) of lateral travel for employees.
A trench 4 feet or deeper needs a way out within 25 feet of lateral travel, which means one ladder every 50 feet of trench if the ladder is in the middle of the run it serves. The calculator counts them, because it is the one quantity on this page that gets forgotten and is trivially cheap to get right.
What the appendix does not cover
Twenty feet. Every configuration in Figure B-1 is stated for excavations 20 feet or less in depth. Past that the appendix gives you nothing and the design has to come from a registered professional engineer under 1926.652(b)(4). This page will not extrapolate the table, because a slope table is not a trend line.
The short-term Type A exception has two conditions, not one. The 1/2:1 slope needs the excavation open 24 hours or less AND 12 feet or less in depth. Miss either and you are back to 3/4:1.
Benching is a separate set of figures. Type A and Type B allow benched configurations with their own maximum bench dimensions, and Type C does not allow benching at all. This page calculates the simple slope only, which is the shape a small job digs.
And none of this is the whole standard. Subpart P also covers water accumulation, adjacent structures, hazardous atmospheres, daily inspection by a competent person and the underground utilities you are required to locate before you break ground. A volume calculator is not a substitute for reading it.
The sources, and what this page is not
Read 2026-09-09. All three are the federal construction standard as published by OSHA and the Office of the Federal Register.
29 CFR 1926.652, Requirements for protective systems, Occupational Safety and Health Administration, Part 1926 Subpart P, Excavations. Source 54 FR 45959, 31 October 1989. Sets the five foot trigger, the stable rock exception, and the four options for designing a sloping or benching system. Option (1) is the one that matters to a calculator: without soil classification, the slope defaults to 1 1/2:1.
Appendix B to Subpart P of Part 1926, Sloping and Benching, Figure B-1, Slope Configurations. All slopes stated in the horizontal to vertical ratio. Gives the maximum allowable slope for each soil type, all of them for excavations 20 feet or less in depth. Beyond 20 feet the appendix does not apply and the design has to come from a registered professional engineer.
29 CFR 1926.651, Specific excavation requirements, Occupational Safety and Health Administration, paragraphs (c)(2) and (j)(2). The egress rule for trenches 4 feet or more in depth, and the two foot setback that decides where the spoil heap is allowed to sit.
This is a workplace safety standard, and it applies to employees. Digging a trench in your own garden with nobody employed is outside its scope, and the physics of a cave-in is not. The figures are here because they are the only published, dated, checkable answer to how far back a face has to be laid, and a wall of soil does not know who is paying you.
Soil classification is not something a web page can do. Appendix A requires at least one visual and one manual test by a competent person, on the material actually exposed. The dropdown above records a classification somebody made; it does not make one.
Frequently asked questions
How do you calculate excavation volume?
Not with length times width times depth, unless the sides are vertical. For a sloped excavation the shape is a frustum: bottom area L by W, top area (L + 2rD) by (W + 2rD), where r is the maximum allowable slope for the soil. The prismatoid rule, D/6 times the bottom area plus four times the mid-depth area plus the top area, is exact for that shape.
How deep can a trench be before it needs shoring?
29 CFR 1926.652(a)(1) requires a protective system for every employee in an excavation, except where the excavation is entirely in stable rock, or is less than 5 feet deep and a competent person's examination of the ground shows no indication of a potential cave-in. So five feet is the trigger, and under five feet is a competent person's judgement rather than an exemption.
What is the OSHA slope for Type C soil?
One and one half horizontal to one vertical, which is 34 degrees from horizontal, for simple slope excavations 20 feet or less in depth. It is also the slope 1926.652(b)(1) requires from any employer who has not classified the soil at all, which makes it the honest default for a calculator.
What is the difference between Type A, B and C soil?
Unconfined compressive strength and condition. Type A is cohesive soil at 1.5 tons per square foot or greater, but nothing is Type A if it is fissured, subject to vibration from traffic or pile driving, or previously disturbed. Type B is cohesive soil between 0.5 and 1.5 tsf plus granular cohesionless soils such as angular gravel, silt and sandy loam. Type C is cohesive soil at 0.5 tsf or less, granular soils including gravel and sand, and anything submerged or freely seeping.
How much does excavation cost per cubic yard?
The source quoted on this page gives 60 to 200 dollars per cubic yard for cut and fill excavation, written by a named author and published 27 December 2025. That is a national range from one publisher, not a quote, and this site publishes no price of its own. The point of pairing it with the volume above is that the sloped volume is several times the box, so the same rate produces a very different budget.
How much bigger is the spoil heap than the hole?
Bigger, and by an amount nobody publishes for your soil. Digging breaks the structure the material had in the ground and air gets in between the clods, so the same soil takes more space. The allowance on this page defaults to 25%, it is this page's own figure and it is an input. A geotechnical report for your site will have a real number in it.
Do I need a ladder in a trench?
1926.651(c)(2) requires a stairway, ladder, ramp or other safe means of egress in trench excavations 4 feet or more in depth, positioned so no employee has more than 25 feet of lateral travel to reach one. That works out at one every 50 feet of trench if each sits in the middle of the run it serves, which is what the calculator counts.
How far from the trench does the spoil have to be?
At least 2 feet from the edge under 1926.651(j)(2), or retained by a device sufficient to stop it rolling in. Worth knowing before you dig on a narrow site, because the heap is larger than the hole and it also acts as a surcharge load, which a competent person has to allow for by flattening the slope further.
Check these numbers yourself
29 CFR 1926.652, Requirements for protective systemsOccupational Safety and Health Administration, Part 1926 Subpart P, Excavations. Source 54 FR 45959, 31 October 1989, read 2026-09-09. The five foot trigger, the stable rock exception, and the four options for designing a sloping system, of which Option (1) sets the 1 1/2:1 default.
Appendix B to Subpart P of Part 1926, Sloping and BenchingOffice of the Federal Register, eCFR, read 2026-09-09. Figure B-1 gives the maximum allowable slope for each soil type, all of them stated for excavations 20 feet or less in depth. Beyond 20 feet the appendix does not apply.
29 CFR 1926.651, Specific excavation requirementsOccupational Safety and Health Administration, read 2026-09-09. Paragraph (c)(2) is the egress rule for trenches 4 feet or more in depth; paragraph (j)(2) is the two foot setback for spoil and equipment.
Lawn Love, how much does land grading costWritten by Sinziana Spiridon, updated 27 December 2025, read 2026-09-09. Gives excavation at 60 to 200 dollars per cubic yard, fill dirt at 6 to 17, plus grading rates per square foot, per acre and per hour, and equipment hire without an operator.
How every figure here is verified: Sources & Method. Who builds this: About. Found something wrong? Tell us and it gets fixed or removed.
Figures on this page last checked against the source documents on 2026-09-09. Codes are amended locally; confirm against the edition your jurisdiction enforces.
The slope figures are the federal construction standard, not this page's. 29 CFR 1926 Subpart P and its Appendix B, read 9 September 2026. They are maximum allowable slopes for the most favourable site conditions, and a competent person is required to flatten them further where there are signs of distress or a surcharge load. Soil classification cannot be done by a web page: Appendix A requires at least one visual and one manual test on the material actually exposed. The bulking allowance is this page's own figure and is an input. Nothing here is a protective system design.