Can I use this instead of the individual calculators?

For sizing a whole deck, yes. Each dedicated page still carries the full code table, the worked example and the reasoning, so use those when you want to see the table the number came from or check a single member in isolation.

Why is my post height different from the height I entered?

The height you enter is to the deck surface. DCA 6 Table 4 measures post height to the underside of the beam, so the joist depth and the decking thickness are subtracted. Both are shown in the result.

What if no joist size spans my deck?

The page says so rather than picking one. Reduce the width, move the joists to 12 in centres, change species, or use an engineered joist, which is outside IRC Table R507.6.

Does it size the ledger?

No, and neither does any other page here. Ledger attachment is IRC R507.9, and it is the connection that actually fails on collapsed decks. Take it to your building department.

Is the material list a shopping list?

It is a takeoff: counts and lengths from your dimensions. It carries no prices, because lumber pricing is regional and moves weekly, and a stale price is worse than none.

Why does changing species change so much?

Because it changes three tables at once. Southern pine spans further as a joist, further as a beam, and carries a taller post, so a species change can move the joist size, the post count and the whole footing schedule together.

Home › Decking › Deck Materials Calculator

Deck Materials Calculator

Source: IRC R507.5(1), R507.6, R312, R311.7 · AWC DCA 6 Tables 4 and C4A

Enter the deck once. This sizes every member against the table that governs it, says which checks pass, and gives you the takeoff, on one page you can print.

Whole deck

Deck width (house out to the beam)

Deck length (along the house)

Deck surface height (above grade)

Species

Joist spacing

Beam size

Board width (actual, 5/4x6 is 5.5)

Gap between boards

Decking thickness

Footing depth (12 in min, or below frost)

Concrete bag yield (60 lb is 0.45, 80 lb is 0.60)

cu ft

IRC Table R507.5(1) beams, R507.6 joists, R312 guards, R311.7 stairs, and AWC DCA 6 Tables 4 and C4A for posts and footings. 40 psf live, 10 psf dead, No. 2 grade, wet service. A ledger-attached rectangular deck.

Specification summary

Generated from on . Reopen that address to reproduce these figures exactly.

Entered

Result

How beam span and joist span are measured

Worked example

A 12 ft by 16 ft ledger-attached deck in Douglas fir-larch, deck surface 8 ft above grade, joists at 16 in centres.

Joists first. The joists span the 12 ft width. IRC Table R507.6 is read at the 16 in column, and the smallest size that reaches 12 ft is taken.
Then the beam. The beam carries a 12 ft joist span, so Table R507.5(1) is read at its 12 ft column. That maximum span divided into the 16 ft length gives the bays, and the bays give the post count and spacing.
Then the posts. Post height is the deck surface less the joist depth and the decking thickness, because that is what DCA 6 Table 4 measures to. That height is checked against the 6x6 limit for this beam span, joist span and species.
Then the footings. The same Table 4 row gives the diameter and thickness, and the entered depth gives the concrete volume.
Then the rest. Board rows, screw count at two per crossing, whether a guard is required at all, and the stair riser count from the same surface height.

Change the species to ponderosa pine or SPF and the post check is the first thing to fail: the same span that allows an 11 ft Douglas fir-larch post allows 5 ft in SPF.

The formula

Nothing here is a new calculation. Each member is the same table lookup the dedicated page performs, run in the order a deck is built, with the output of one becoming the input of the next:

joist span → beam column → beam span → post spacing → post height limit & footing size

Joists: IRC Table R507.6 at your spacing. The smallest size that spans the width
Beam: IRC Table R507.5(1) at the joist-span column. Its span sets the bays
Posts: AWC DCA 6 Table 4, keyed on beam span and joist span
Footings: The same Table 4 row, which carries diameter and thickness
Guard: IRC R312, required once the surface is over 30 in above grade
Stairs: IRC R311.7.5.1, risers at 7 3/4 in maximum

The order matters, because each step constrains the next. A wider deck pushes the joist size up, which pushes the beam column across, which shortens the allowed beam span, which adds posts, which changes the footing schedule.

Where this page is deliberately conservative

The three tables group species differently. IRC Table R507.5(1) puts everything except southern pine in a single bucket. R507.6 puts hem-fir with Douglas fir but western cedars in another group, and spruce-pine-fir with Douglas fir but ponderosa and red pine elsewhere. DCA 6 Table 4 lists five groups. Where your species could sit in two of them, this page takes the shorter span. Erring short is the safe direction on a member that holds people off the ground.

It assumes a rectangular deck attached to the house by a ledger. A wrapped, angled, multi-level or freestanding deck changes the load path and the post count, and neither the tables nor this page covers it.

Post height is derived, not entered. The deck surface height you enter, less the joist depth and the decking thickness, is the height to the underside of the beam, which is what Table 4 measures to. If your framing differs, use the post calculator directly.

The stair figure is the riser count only. It divides the same surface height by the 7 3/4 in maximum. Landings, headroom, the vertical rise limit and the stringer layout are on the stair page, not here.

Ledger attachment is not checked at all. IRC R507.9 governs it, and ledger failure rather than decking failure is what collapses decks. No calculator on this site sizes a ledger connection.

What this page does not check

It sizes members against prescriptive tables. It is not an engineered design, and the following are outside it entirely: ledger attachment and its bolt pattern (IRC R507.9), lateral load connection (R507.2.3), beam-to-post connection hardware, footing bearing capacity below the assumed 1,500 psf, frost depth, seismic and high-wind provisions, guard post attachment under the 200 lb load, stair landings and headroom, and anything carrying a hot tub, a planter, a roof or a second storey.

Every one of those has failed a real deck. The ones this page can point you at have their own calculator; the ones it cannot are a conversation with your building department or an engineer.

Why the order is the answer

Most deck calculators answer one question at a time, which hides the thing that actually bites: the answers are chained. Widen a deck by two feet and the joist size goes up, which moves the beam table across a column, which shortens the beam's allowed span, which adds a post, which changes every footing. A page that sizes the joist without re-running the beam has given you a number that was true before you moved the wall.

That is why this page exists and why it runs in build order. Each dedicated calculator still holds the full table, the worked example and the provenance for its own member. Use them when you want to see the table; use this when you want to know whether the whole thing stands up.

Frequently asked questions

Can I use this instead of the individual calculators?: For sizing a whole deck, yes. Each dedicated page still carries the full code table, the worked example and the reasoning, so use those when you want to see the table the number came from or check a single member in isolation.
Why is my post height different from the height I entered?: The height you enter is to the deck surface. DCA 6 Table 4 measures post height to the underside of the beam, so the joist depth and the decking thickness are subtracted. Both are shown in the result.
What if no joist size spans my deck?: The page says so rather than picking one. Reduce the width, move the joists to 12 in centres, change species, or use an engineered joist, which is outside IRC Table R507.6.
Does it size the ledger?: No, and neither does any other page here. Ledger attachment is IRC R507.9, and it is the connection that actually fails on collapsed decks. Take it to your building department.
Is the material list a shopping list?: It is a takeoff: counts and lengths from your dimensions. It carries no prices, because lumber pricing is regional and moves weekly, and a stale price is worse than none.
Why does changing species change so much?: Because it changes three tables at once. Southern pine spans further as a joist, further as a beam, and carries a taller post, so a species change can move the joist size, the post count and the whole footing schedule together.

Check these numbers yourself

IRC R507.5 and R507.6: deck beams and joistsUpCodes. The two span tables this page reads for the beam and the joists.
AWC DCA 6: Prescriptive Residential Wood Deck Construction GuideAmerican Wood Council, free PDF. Table 4 for post heights and footing sizes, Table C4A for 4x4.
IRC R312: guardsUpCodes. When a guard is required and the limits that apply to it.
IRC R311.7: stairwaysUpCodes. The riser maximum this page divides by.

Figures on this page last checked against the source documents on 2026-09-06. Codes are amended locally; confirm against the edition your jurisdiction enforces.

Related calculators

Estimates only. This applies prescriptive tables to a rectangular ledger-attached deck at 40 psf live and 10 psf dead, No. 2 grade, wet service. It is not an engineered design and it does not check ledger attachment, lateral load connection, connector hardware, soil bearing below 1,500 psf, frost depth, seismic or wind provisions, guard post attachment, or stair landings and headroom. Confirm the adopted code edition and every dimension with your building department before you build.