About Deck & Fence Stain Calculator (Gallons)
The deck and fence stain calculator turns real coating geometry into gallons to buy. Fences are the classic under-estimate: staining both sides of a 6-ft privacy fence doubles the area, so 100 ft of fence is 1,200 ft² of wood — not 600. Decks add railing area the same way: every lineal foot of railing carries surface on both faces. Enter the geometry, pick one or two coats, and the tool pools the whole job before rounding, so two coats that each need two and a half gallons buy five gallons, not six.
Coverage is seeded from a named datasheet — Behr's Premium Semi-Transparent Waterproofing Stain & Sealer No. 5077 publishes 250–300 ft² per gallon for the first coat and a thinner second coat at roughly 500–600 ft²/gal — and the calculator seeds the midpoints (275 and 550) while leaving both rates editable, because rough-sawn, weathered, or thirsty wood drinks at the bottom of any published range and your product's own TDS governs. This tool covers exterior wood stain geometry; interior room painting lives in the paint coverage calculator and asphalt sealing in the driveway sealer calculator.
How It Works
- Pick fence or deck mode. Fence: enter the run length, the height, and whether you are coating one side or both — both sides is the durability play and exactly doubles the area. Deck: enter the walking-surface area, then the railing as lineal feet and height; the calculator counts both railing faces.
- Choose coats. Most semi-transparent products, including the seeded Behr 5077, require two coats for optimal appearance and durability — the first coat soaks in at the low spread rate, the thinner second coat spreads roughly twice as far, and the calculator uses each coat's own rate.
- Adjust the coverage rates to your product's TDS. The seeds are the midpoints of the published Behr 5077 ranges; smooth planed wood lands at the top of a range, rough or weathered wood at the bottom. Solid stains and clear sealers publish different ranges — type them in.
- Read the result: exact gallons, the whole-gallon buy (pooled across coats before rounding up, so per-coat remainders don't each buy their own can), and a suggested split into 5-gallon pails and 1-gallon cans.
- Prep governs the outcome: coverage numbers assume clean, dry, absorbent wood. New pressure-treated lumber usually needs to weather before it will take stain, and a splash test (water beads = not ready) is the cheap insurance before you open the first can.
Worked Example
A 60-ft cedar privacy fence, 6 ft tall, gets one maintenance coat on both sides: 60 × 6 × 2 = 720 ft². At the seeded 275 ft²/gal first-coat rate that is 720 ÷ 275 = 2.62 gallons — buy 3 one-gallon cans. Doing the full two-coat system instead would add 720 ÷ 550 = 1.31 gallons for the thin second coat, pooling to 3.93 gallons total — 4 gallons, still cheaper than the 5 you would buy rounding each coat separately at a store that talks you into per-coat math.
Formulas
- Area to coat
fence: A = L × H × sides; deck: A = A_deck + L_rail × H_rail × 2- Gallons (pooled across coats)
gal = A/C₁ + A/C₂ (coat 2 only), rounded UP once
Standards & References
- BEHR PREMIUM Semi-Transparent Waterproofing Stain & Sealer No. 5077, Technical Data Sheet (2/1/2017 compliance revision) — coverage 250–300 ft²/gal first coat, ~500–600 ft²/gal thinner second coat, 2 coats required (seeded midpoints, editable)
- Coating geometry — definitional area arithmetic (run × height × sides; railing both faces)
Frequently Asked Questions
How much stain do I need for a fence?
Multiply run length × height × sides coated, then divide by your product's coverage. A 100-ft, 6-ft-tall fence stained on both sides is 1,200 ft²; at the typical 275 ft²/gal first-coat rate that is about 4.4 gallons — a 5-gallon pail — per coat. Staining only the street side halves it. Rough-sawn fence boards drink at the low end of the published range.
Do I really need two coats of deck stain?
Most semi-transparent stain-and-sealer products specify two coats — the seeded Behr 5077 TDS says two coats are required for optimal appearance and durability. The second coat is applied thinner and spreads roughly twice as far (about 500–600 ft²/gal vs 250–300 for the first), so it adds only about half the first coat's gallons. One-coat products and maintenance recoats on sound finishes are the exceptions.
How many square feet does a gallon of stain cover?
The seeded datasheet publishes 250–300 ft² per gallon on the first coat — smooth wood at the top, rough or weathered wood at the bottom — and roughly double that for the thin second coat. Solid-color stains and film-forming finishes publish their own (usually similar) ranges; enter your can's number since the calculator's rate is fully editable.
Should I count both sides of the fence and railing?
If you are coating them, yes — the wood does not care that it is the same fence. Both sides of a fence doubles the area exactly, and railings carry surface on both faces plus balusters; the calculator's lineal-feet × height × 2 railing model approximates a typical baluster railing's wetted area. Skipping the neighbor's side halves the fence area but leaves that face unprotected.
Is this calculator for paint or driveway sealer too?
No — it is for exterior wood stain and sealer geometry (fences, decks, railings). Interior wall and ceiling painting, with its room-perimeter math and door/window subtractions, is the paint coverage calculator's job; asphalt driveway sealing in 5-gallon pails by surface condition is the driveway sealer calculator's. Cross-check your fence post and picket counts with the fence materials calculator before you buy.