How much stain do I need for a 16×20 deck?

Data checked October 2026

Short answer

A 16×20 ft deck with railings and 3 steps is 675 sq ft of wood — 6.75 gallons for two coats of semi-transparent stain, so buy 7 gal.

Floor: 16 × 20 = 320 sq ft. Railing: 56 ft × 3 ft × 2.0 for balusters = 336 sq ft. Stairs: 3 steps × 4 ft × (11 in tread + 7¾ in riser) = 19 sq ft.
Two coats at 200 sq ft/gal on weathered wood: 675 × 2 ÷ 200 = 6.75 gal → 7 gal (about $406).
Floor only (no railings or stairs): 3.2 gal — buy 3 gal + 1 qt.
Sherwin-Williams' deck calculator (250 sq ft/gal) says 5.4 gal for two coats; Olympic's rule of thumb says 3–4 gallons for this area.
A 16×20 deck holds dining and lounge areas. Even at this size the balustered railing takes about as much stain as the floor, and a pump sprayer plus back-brushing saves real time.

Adjust it to your exact job

What are you staining?

Project

Deck length

= 16' · 4.88 m

Deck width

= 20' · 6.1 m

Railings

Railing length

= 56' · 17.07 m

Railing height

= 3' · 0.91 m

Balusters / spindles

Spindles have 4 faces each: Sherwin-Williams counts railing area × 2.0 with them, × 0.6 without.

Stair steps

Stair width

= 4' · 1.22 m

Stain

Type

Product

200 sq ft per gallon per coat, a conservative planning figure below most makers' ranges. Check the can — some semi-transparents are one-coat products.

Wood condition

Coats

Buy

7 galof stain

6.75 gal for 675 sq ft · coat 1 at 200 sq ft/gal, later coats at 200 · $406

Deck boards: 320sq ft
Railings: 336sq ft× 2.0 for spindles
Stairs: 19sq ft3 treads + risers
Stain + supplies: $509$406 stain

Other semi-transparent stains on this job

Same area, each product at its own label coats and coverage, cheapest first
Product	Coats	Gallons	Buy	Cost
Thompson's WaterSeal Semi-Transparent Wood Sealer	1	4.5	4 gal + 2 qt	$139
Benjamin Moore Woodluxe Semi-Transparent (0692)	1	2.25	2 gal + 1 qt	$144
Sherwin-Williams SuperDeck Semi-Transparent	1	3.37	3 gal + 2 qt	$195
Cabot Semi-Transparent Stain & Sealer (oil)	1	3.37	3 gal + 2 qt	$220
Behr Premium Semi-Transparent (No. 5077)	2	3.6	4 gal	$232
Ready Seal Exterior Wood Stain & Sealer	1	4.5	4 gal + 2 qt	$278
Valspar One Coat Semi-Transparent	1	4.5	4 gal + 2 qt	$278
Olympic Elite Semi-Transparent	2	5.4	5 gal + 2 qt	$336
Defy Extreme Semi-Transparent	2	6.75	1 × 5 gal + 2 gal	$390
Typical semi-transparent stain	2	6.75	7 gal	$406

Compared with Sherwin-Williams' deck calculator

It assumes 250 sq ft/gal for every stain and wood and says 5.4 gal for 2 coats. We use this product's data-sheet rate for weathered wood.

Olympic's rule of thumb says 3–4 gallons for 675 sq ft in any transparency — handy, but it ignores coats and wood condition, so we use each product's data sheet instead.

Test the spread first

Stain soaks into dry, weathered wood far faster than into new boards. Do one board run, see how far a gallon really goes, then buy the rest — unopened cans are easier to return than mixed tints.

Shopping list

7 cans Typical semi-transparent stain — 1-gal can (deck)$406
1 packs 9 in roller covers, 3-pack, 3/8 in napa fresh cover for each product or color$6.43
1 kit Roller frame & tray kit$21.94
1 brush 2½ in angled sash brushfor cutting in$13.94
1 pole Extension polefor a roller or stain pad on the floor$35.99
1 jug Deck & wood cleaner / brightenerclean (and strip old coatings) first; check the label's coverage
1 cloth Canvas drop cloth, 9 × 12 ftprotect siding, plants and pavers from drips$24.97

Estimated total$509

Cost estimate

Tap a price to use your store's

Typical semi-transparent stain, 1-gal can (deck)
7 cans × $typical price — no verified listing
$406
9 in roller covers, 3-pack, 3/8 in nap
1 packs × $
$6.43
Roller frame & tray kit
1 kit × $
$21.94
2½ in angled sash brush
1 brush × $
$13.94
Extension pole
1 pole × $
$35.99
Canvas drop cloth, 9 × 12 ft
1 cloth × $
$24.97

Materials total$509

Prices checked October 23, 2026 (maker and Walmart.com listings). Typical prices are labelled; tap any price to enter your store's.

Did this answer your question?

Compare

Stain for this 16×20 deck by product type (each at its label coats)

Stain	Coats	Gallons	Buy	Cost
Thompson's WaterSeal Clear Wood Sealer	1	3.37 gal	3 gal + 2 qt	$75.78
Typical semi-transparent stain	2	6.75 gal	7 gal	$406
Ready Seal Exterior Wood Stain & Sealer	1	4.5 gal	4 gal + 2 qt	$278
Behr Premium Solid Color (No. 5011)	2	5.06 gal	5 gal + 1 qt	$313
Cabot DeckCorrect resurfacer	2	9 gal	9 gal	$522

How this was worked out

Many semi-transparent stains are one-coat products — a second coat sits on top and peels. Check the can before buying for two coats.

The full method, material data and tips are on the main deck stain calculator page.

Similar jobs

Other sizes people check

Sources

Data behind this answer

Sherwin-Williams Paint Calculator (help text and AjaxPaintCalculator responses) — results are per coat at 400 (interior), 350 (exterior) and 250 (deck) sq ft/gal; 3×7 ft doors and 3×5 ft windows; trim area = LF × height subtracted from the wall; railings × 0.6, or × 2.0 with spindles; gables = width × peak ÷ 2 · checked October 2026
Sherwin-Williams SuperDeck semi-transparent — PDS 114.80 (06/2020) — smooth 350, rough/porous 100–200 sq ft/gal · checked October 2026
Sherwin-Williams WoodScapes Solid Color — PDS 105.11 — 200–400 sq ft/gal, 2 coats · checked October 2026
Benjamin Moore Woodluxe 0691–0694 — TDS — 300–400 sq ft/gal; translucent/semi one coat, solid 1–2 · checked October 2026
Behr Premium Semi-Transparent Waterproofing Stain & Sealer No. 5077 — TDS (rev. 7/2024) — first coat 300 sq ft/gal, thinner second coat 500; two coats required · checked October 2026
Behr Premium Solid Color Waterproofing Stain & Sealer No. 5011 — TDS (rev. 1/2023) and label — 200–400 sq ft/gal (label: 2nd coat 400–800); excludes spray loss; 35–90°F · checked October 2026
Olympic Elite Semi-Transparent — TDS 802102 — 250–350 sq ft/gal; two coats recommended; 35–90°F · checked October 2026
Olympic Elite Solid Color — TDS 80301 — 350–500 sq ft/gal; two thin coats · checked October 2026
Olympic — How much stain for a deck or patio — ≤175 sq ft 1 gal; ≤550 2 gal; ≤700 3–4 gal · checked October 2026
Cabot Semi-Transparent Stain & Sealer — product page — 200–650 sq ft/gal; 1 coat only · checked October 2026
Cabot Solid Color Acrylic — product page — 200–500 sq ft/gal; 2 coats · checked October 2026
Cabot Australian Timber Oil — product page — 250–600 sq ft/gal; one coat · checked October 2026
Cabot DeckCorrect — product page and retailer specs — 75 sq ft/gal for the required two coats; 50–90°F · checked October 2026
Thompson's WaterSeal tinted wood sealers — product pages — 150–400 sq ft/gal; 1 coat; semi-transparent $28.98 at Walmart · checked October 2026
Thompson's WaterSeal Clear Wood Sealer — product page — 200–400 sq ft/gal; one light coat; $19.94 gal / $92.87 5 gal at Walmart · checked October 2026
Ready Seal — TDS (rev. 05/12/2026) and 2026 application instructions — practical 125–175 sq ft/gal; cedar/treated pine deck 150, rough cedar 125; ≤12% wood moisture · checked October 2026
Defy Extreme & Defy Solid — product pages — Extreme 100–150 sq ft/gal (100 for 2 coats); Solid 200–300 per coat; $59.99 / $66.96 gal · checked October 2026
Valspar One Coat Semi-Transparent Stain — product page — 150–400 sq ft/gal; 1 coat; 50–90°F · checked October 2026
International Residential Code — R311.7.5 stair treads & risers (Boise IRC handout) — 7¾ in maximum riser, 10 in minimum tread · checked October 2026
Painting supplies — Walmart.com listings — ScotchBlue 60 yd $7.88; 9×12 canvas drop cloth $24.97; 3-pack roller covers $6.43; tray kit $21.94; 2½ in sash brush $13.94 · checked October 2026

Short answer

A 16×20 ft deck with railings and 3 steps is 675 sq ft of wood — 6.75 gallons for two coats of semi-transparent stain, so buy 7 gal.

Floor: 16 × 20 = 320 sq ft. Railing: 56 ft × 3 ft × 2.0 for balusters = 336 sq ft. Stairs: 3 steps × 4 ft × (11 in tread + 7¾ in riser) = 19 sq ft.

Two coats at 200 sq ft/gal on weathered wood: 675 × 2 ÷ 200 = 6.75 gal → 7 gal (about $406).

Floor only (no railings or stairs): 3.2 gal — buy 3 gal + 1 qt.

Sherwin-Williams' deck calculator (250 sq ft/gal) says 5.4 gal for two coats; Olympic's rule of thumb says 3–4 gallons for this area.

A 16×20 deck holds dining and lounge areas. Even at this size the balustered railing takes about as much stain as the floor, and a pump sprayer plus back-brushing saves real time.

Adjust it to your exact job

What are you staining?

Project

Deck length

= 16' · 4.88 m

Deck width

= 20' · 6.1 m

Railings

Railing length

= 56' · 17.07 m

Railing height

= 3' · 0.91 m

Balusters / spindles

Spindles have 4 faces each: Sherwin-Williams counts railing area × 2.0 with them, × 0.6 without.

Stair steps

Stair width

= 4' · 1.22 m

Stain

Type

Product

200 sq ft per gallon per coat, a conservative planning figure below most makers' ranges. Check the can — some semi-transparents are one-coat products.

Wood condition

Coats

Buy

7 galof stain

6.75 gal for 675 sq ft · coat 1 at 200 sq ft/gal, later coats at 200 · $406

Deck boards: 320sq ft
Railings: 336sq ft× 2.0 for spindles
Stairs: 19sq ft3 treads + risers
Stain + supplies: $509$406 stain

Other semi-transparent stains on this job

Same area, each product at its own label coats and coverage, cheapest first
Product	Coats	Gallons	Buy	Cost
Thompson's WaterSeal Semi-Transparent Wood Sealer	1	4.5	4 gal + 2 qt	$139
Benjamin Moore Woodluxe Semi-Transparent (0692)	1	2.25	2 gal + 1 qt	$144
Sherwin-Williams SuperDeck Semi-Transparent	1	3.37	3 gal + 2 qt	$195
Cabot Semi-Transparent Stain & Sealer (oil)	1	3.37	3 gal + 2 qt	$220
Behr Premium Semi-Transparent (No. 5077)	2	3.6	4 gal	$232
Ready Seal Exterior Wood Stain & Sealer	1	4.5	4 gal + 2 qt	$278
Valspar One Coat Semi-Transparent	1	4.5	4 gal + 2 qt	$278
Olympic Elite Semi-Transparent	2	5.4	5 gal + 2 qt	$336
Defy Extreme Semi-Transparent	2	6.75	1 × 5 gal + 2 gal	$390
Typical semi-transparent stain	2	6.75	7 gal	$406

Compared with Sherwin-Williams' deck calculator

It assumes 250 sq ft/gal for every stain and wood and says 5.4 gal for 2 coats. We use this product's data-sheet rate for weathered wood.

Olympic's rule of thumb says 3–4 gallons for 675 sq ft in any transparency — handy, but it ignores coats and wood condition, so we use each product's data sheet instead.

Test the spread first

Stain soaks into dry, weathered wood far faster than into new boards. Do one board run, see how far a gallon really goes, then buy the rest — unopened cans are easier to return than mixed tints.

Shopping list

7 cans Typical semi-transparent stain — 1-gal can (deck)$406
1 packs 9 in roller covers, 3-pack, 3/8 in napa fresh cover for each product or color$6.43
1 kit Roller frame & tray kit$21.94
1 brush 2½ in angled sash brushfor cutting in$13.94
1 pole Extension polefor a roller or stain pad on the floor$35.99
1 jug Deck & wood cleaner / brightenerclean (and strip old coatings) first; check the label's coverage
1 cloth Canvas drop cloth, 9 × 12 ftprotect siding, plants and pavers from drips$24.97

Estimated total$509

Cost estimate

Tap a price to use your store's

Typical semi-transparent stain, 1-gal can (deck)
7 cans × $typical price — no verified listing
$406
9 in roller covers, 3-pack, 3/8 in nap
1 packs × $
$6.43
Roller frame & tray kit
1 kit × $
$21.94
2½ in angled sash brush
1 brush × $
$13.94
Extension pole
1 pole × $
$35.99
Canvas drop cloth, 9 × 12 ft
1 cloth × $
$24.97

Materials total$509

Prices checked October 23, 2026 (maker and Walmart.com listings). Typical prices are labelled; tap any price to enter your store's.

Stain

Coats

Gallons

Buy

Cost

Thompson's WaterSeal Clear Wood Sealer

3.37 gal

3 gal + 2 qt

$75.78

Typical semi-transparent stain

6.75 gal

7 gal

$406

Ready Seal Exterior Wood Stain & Sealer

4.5 gal

4 gal + 2 qt

$278

Behr Premium Solid Color (No. 5011)

5.06 gal

5 gal + 1 qt

$313

Cabot DeckCorrect resurfacer

9 gal

$522