How much stain do I need for a 16x12 deck?

About 514 sq ft of surface if it has a three-sided railing and a four-step flight, not the 192 sq ft the floor measures. At the 450 sq ft per gallon Cabot publishes for smooth wood that is 1.1 gallons, so two cans. At the 200 sq ft per gallon it publishes for rough or weathered wood it is 2.6 gallons, so three.

How many square feet does a gallon of deck stain cover?

It depends far more on the wood than the brand. Cabot's #300 series publishes 450 to 650 sq ft per gallon on smooth surfaces and 200 to 300 on rough. Sherwin-Williams SuperDeck solid colour publishes 200 to 400 and states the figure depends on the porosity and texture of the wood.

Do I need to include the railing when calculating deck stain?

Yes, and on a typical deck it is larger than the floor. Forty feet of railing at 36 in with balusters at 5 in on centre works out at 221 sq ft: 122 for the 96 balusters at four faces each, 50 for the top and bottom rails, and 49 for eight 6x6 posts.

Is a second coat of deck stain the same quantity as the first?

No, it is less. The first coat partly seals the wood, so the second goes further. TWP publishes 150 to 200 sq ft per gallon for the first coat and 200 to 300 for the second. Where a manufacturer does not publish a second-coat figure, using the first-coat rate for both over-buys slightly, which is the safe direction.

Should I buy from the high or low end of the coverage range?

The low end. A spare gallon is a modest cost and keeps for its shelf life. Running out three quarters of the way across a deck means the stain you already laid has begun to set, and the lap mark where you restart will not sand out.

Why do you not list Behr or Olympic coverage?

Because no manufacturer data sheet for either could be obtained from here. The figures circulating for both sit on review sites and retailer listings, and repeating a number does not source it. Read the back of your can and type the figure into the override field.

Does stain coverage change on composite decking?

Composite is not stained. It is a capped or uncapped plastic composite and manufacturers void warranties for coating it. If you are working out board quantities for composite, the composite decking calculator handles that instead.

Home › Decking › Deck Stain Calculator

Deck Stain Calculator

Counts board edges, balusters and stairs. Coverage from the data sheets.

Every deck stain calculator asks for length and width and divides by a coverage number. So does Cabot's own data sheet. But a railed deck with a flight of stairs has board edges, four faces on every baluster, rails, posts, treads, risers and stringers, and none of that is in length times width. This counts the lot, then sizes the order from the thirsty end of the published range.

Deck stain quantity

Stain and surface

Coats

Deck length

Deck width

Board width (actual)

Gap between boards

Board thickness (5/4 board is 1 in)

Railing

Railing height

Baluster spacing (on centre)

Baluster width

Stair steps

no.

Stair width

Coverage from your can (optional, overrides)

sq ft/gal

Coverage comes from the manufacturer's product data sheet, named in the table below. If you have the can, use the override field: the label beats this page.

Specification summary

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

Entered

Result

Where the stained surface actually is

Worked example

A 16 ft by 12 ft deck, 5/4 boards at a 3/16 in gap, railing on three sides at 36 in, balusters at 5 in on centre, and a four-step flight 4 ft wide.

The floor. 16 × 12 = 192 sq ft. This is the only number most calculators want, and it is where they stop.
Board edges. 26 rows, both edges exposed, 16 ft long, 1 in deep: 69 sq ft, or 36% on top of the floor before anything is stood on it.
Railing. 40 ft of rail, 96 balusters at four faces each, 8 posts: 221 sq ft. More than the deck floor, and the slowest part to coat.
Stairs. Four steps at 4 ft wide, treads, risers and both stringer faces: 31 sq ft.
Total. 514 sq ft against 192. Sizing from length times width buys 168% too little stain.

That is not a rounding error, the real surface is nearly three times the floor. Set the railing to none and the stairs to zero and the gap falls to 36%, all of it board edges: on a bare floating deck the old method is nearly right, which is presumably how it survived.

The formula

Four surfaces, added up. The girth figures are spelled out rather than hidden in a constant, so you can substitute your own sections:

A = LW + 2 n L t/12 + R g + 4 b w h/144 + S gallons = A / c

LW: the deck floor, and the only term most calculators use
n, t: board rows and board thickness, in. Each gap exposes two edges
R, g: railing length, ft, and girth per foot. A 2x6 top rail coated on top and both sides is 8.5 in, a 2x4 bottom rail 6.5 in, so g = 15/12 sq ft per ft
b, w, h: baluster count, width in, and clear length in. Four faces each
S: stairs: per step, tread run 11 in plus riser 7 in plus a 1 in nosing edge, times the width, plus both stringer faces
c: coverage, sq ft per gallon, from the data sheet

Post surface is counted separately, four 5 1/2 in faces per post at 6 ft spacing and 4 in above the rail. On the worked example that is 49 sq ft from eight posts alone. Substitute 4x4 posts and it drops to 31, so posts are worth getting right, but the balusters are still the larger half.

Where the extra surface comes from

A deck is not a floor. It is a floor with several hundred feet of exposed edge, a picket fence stood on top of it, and a short flight of stairs, and all of it takes stain. On the worked example above the parts that are not floor come to more than the floor itself.

Board edges are the term people find most surprising. A 16 ft by 12 ft deck has twenty-six rows of board, each with two long edges standing in the gap, and at a 1 in board thickness that is 69 sq ft of surface. It is also the surface that matters most, because water sits in the gap and edges are where a deck starts to fail.

Balusters are the second. Ninety-six of them at four faces each comes to 122 sq ft, and with the rails and posts the railing reaches 221 sq ft, more than the deck floor it stands on. Anyone who has stained a railing knows it took longer than the deck did.

None of this is a criticism of the manufacturers. Their data sheets are describing a coating, not doing your takeoff. But their worked example is length times width, and that example gets copied into every calculator on the subject.

Published coverage, square feet per gallon
Product and surface	First coat	Second coat	Coats	Document
Cabot Semi-Transparent Stain + Sealer #300, smooth or new wood	450 to 650 sq ft	not published separately	1	Cabot product data sheet
Cabot Semi-Transparent Stain + Sealer #300, rough sawn or weathered	200 to 300 sq ft	not published separately	1	Cabot product data sheet
Sherwin-Williams SuperDeck Waterborne Solid Color Stain (SD7-251)	200 to 400 sq ft	not published separately	2	Sherwin-Williams document 114.70B, 3/2025
TWP wood preservative stain	150 to 200 sq ft	200 to 300 sq ft	2	twpstain.com, bylined TWP Stains, 1 May 2024

Read 2026-09-07. Where a document gives a range, this page sizes an order from the low end.

Download this table as CSV. Same cells as printed above, nothing added.

Why floor area is the wrong number, and by how much

Cabot’s own data sheet tells you how to size the order:

Square feet can be calculated by multiplying length and width; e.g., 10'W x 25'L = 250 sq. ft.

Length times width. That is the deck floor, and on a railed deck with a flight of stairs the floor is often well under half of what your brush actually touches. The stain does not know it is standing on a data sheet.

What length times width leaves out:

Board edges. Every gap between two boards exposes two edges the full length of the deck. Twenty-six rows of 5/4 board on a 16 ft deck is over 60 sq ft of edge, and edges are end-grain-adjacent and drink.
Balusters. A baluster has four faces. Forty of them at 36 in is more surface than a small bathroom floor, and it is the slowest part to coat.
Rails and posts. A top rail is coated on top, both sides and often underneath. A 6x6 post has four faces above the decking.
Stairs. Treads, risers and the exposed face of each stringer. A four-step flight adds more surface than most people allow for.

The calculator prints both figures side by side so you can see the gap on your own deck rather than take the claim on trust.

Coverage is a range, and the wood decides where you land in it

Sherwin-Williams states it plainly on the SuperDeck sheet:

Coverage is dependent on porosity and texture of the wood. Note: New wood normally requires less product than old, weathered wood. This is due to older wood being more porous than newer wood.

Cabot publishes the same fact as two separate numbers, and the size of the gap is the point: 450 to 650 sq ft per gallon on smooth surfaces, 200 to 300 on rough. That is the identical product. A grey, weathered, previously unsealed deck can take more than twice what the same deck took when it was new.

Which is why this calculator sizes your order from the low end of whichever range you pick. Buying a spare gallon costs about forty dollars. Running out three quarters of the way across a deck means the section you already laid has started to set, and the lap mark where you restart does not sand out.

If you have the actual can in front of you, type its number into the override field. The label beats anything on this page.

One coat or two, and why it changes the arithmetic twice

A second coat does not need the same amount as the first. The wood is already partly sealed, so it drinks less, and the published second-coat figure is usually higher than the first. TWP puts the first coat at 150 to 200 sq ft per gallon and the second at 200 to 300: the second coat costs roughly two thirds of the first, not the same again.

Most data sheets do not separate the two at all, so where the figure is not published this calculator uses the first-coat rate for both. That over-buys slightly, which is the correct direction to be wrong in.

Some products are formulated for one coat only, Cabot's #300 series among them. Adding a second to those can leave stain sitting on the surface instead of penetrating, and staying tacky. The calculator warns when you ask for a coat the data sheet does not support.

New wood, weathered wood, and the number that doubles

The single biggest variable is not the brand, it is how thirsty the wood is. Cabot publishes 450 to 650 sq ft per gallon on smooth surfaces and 200 to 300 on rough, for the same product out of the same can. A deck that has been grey and unsealed for three summers can take more than twice what it took when it was new.

Stripping and brightening a weathered deck opens the grain further and can increase uptake again. Sanding closes it and reduces uptake. Neither is a reason to skip the prep, but both change what you should buy, and the only honest way to handle it is to buy from the thirsty end of the range.

Pressure treated lumber straight from the yard is a separate case: it is often too wet to take stain at all, and most manufacturers ask you to wait until it absorbs water rather than beading it.

What this does not cover

The underside of a raised deck, the joists and beam, and the fascia or skirt board are not counted here. Most people do not coat them, but if you are, add the areas yourself: the underside is another length times width, and the fascia is the perimeter times its height.

If you are staining a fence rather than a deck, the surface question is different again, because a fence is coated on both faces. The privacy fence calculator gives the picket count and area to work from.

Where these coverage rates came from

Read 2026-09-07. Coverage figures on this page come from the manufacturer’s product data sheet wherever one could be obtained.

Document	Revision	Kind
Cabot Semi-Transparent Stain + Sealer #300 Series, product data sheet	Cabot product data sheet	Manufacturer data sheet
SuperDeck Exterior Waterborne Solid Color Stain SD7-251 Series	Sherwin-Williams document 114.70B, 3/2025	Manufacturer data sheet
What is the coverage rate for TWP?	twpstain.com, bylined TWP Stains, 1 May 2024	Secondary, see note

Behr and Olympic are missing on purpose. Their coverage figures are quoted all over the web, but every copy traceable from here sat on a review site or a retailer listing rather than on the manufacturer’s data sheet. Repeating a number does not source it. If you are using either brand, read the back of the can and use the override field.

The TWP row is secondary and says so. It is carried because it is the only published source found that separates first-coat coverage from second-coat coverage, which is a distinction the other sheets simply do not make.

Frequently asked questions

How much stain do I need for a 16x12 deck?: About 514 sq ft of surface if it has a three-sided railing and a four-step flight, not the 192 sq ft the floor measures. At the 450 sq ft per gallon Cabot publishes for smooth wood that is 1.1 gallons, so two cans. At the 200 sq ft per gallon it publishes for rough or weathered wood it is 2.6 gallons, so three.
How many square feet does a gallon of deck stain cover?: It depends far more on the wood than the brand. Cabot's #300 series publishes 450 to 650 sq ft per gallon on smooth surfaces and 200 to 300 on rough. Sherwin-Williams SuperDeck solid colour publishes 200 to 400 and states the figure depends on the porosity and texture of the wood.
Do I need to include the railing when calculating deck stain?: Yes, and on a typical deck it is larger than the floor. Forty feet of railing at 36 in with balusters at 5 in on centre works out at 221 sq ft: 122 for the 96 balusters at four faces each, 50 for the top and bottom rails, and 49 for eight 6x6 posts.
Is a second coat of deck stain the same quantity as the first?: No, it is less. The first coat partly seals the wood, so the second goes further. TWP publishes 150 to 200 sq ft per gallon for the first coat and 200 to 300 for the second. Where a manufacturer does not publish a second-coat figure, using the first-coat rate for both over-buys slightly, which is the safe direction.
Should I buy from the high or low end of the coverage range?: The low end. A spare gallon is a modest cost and keeps for its shelf life. Running out three quarters of the way across a deck means the stain you already laid has begun to set, and the lap mark where you restart will not sand out.
Why do you not list Behr or Olympic coverage?: Because no manufacturer data sheet for either could be obtained from here. The figures circulating for both sit on review sites and retailer listings, and repeating a number does not source it. Read the back of your can and type the figure into the override field.
Does stain coverage change on composite decking?: Composite is not stained. It is a capped or uncapped plastic composite and manufacturers void warranties for coating it. If you are working out board quantities for composite, the composite decking calculator handles that instead.

Check these numbers yourself

Cabot Semi-Transparent Stain + Sealer #300 Series, product data sheetCabot, hosted on paintdocs.com. Coverage 450 to 650 sq ft per gallon smooth, 200 to 300 rough.
SuperDeck exterior stains, Sherwin-WilliamsSherwin-Williams. The SuperDeck SD7-251 data sheet, document 114.70B dated 3/2025, gives 200 to 400 sq ft per gallon at 4 to 8 mils wet.
TWP coverage ratetwpstain.com, a dealer site rather than the manufacturer. The only source found that separates first-coat from second-coat coverage.

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 2026-09-07. Codes are amended locally; confirm against the edition your jurisdiction enforces.

Related calculators

The can beats this page. Coverage rates were read from the documents named above on 7 September 2026 and manufacturers revise them. Surface figures assume common section sizes, listed in the formula, and your deck may differ. Buy a spare gallon.