Loan Deck Stain Estimator
A deck drinks stain like a sponge the first time and sips it the second — and the railings you forget to count hold nearly a third of the surface. Enter the deck, the wood condition, coats and railing length: get gallons and quarts.
Railing length is the total run of railing you will stain — measure the open sides. The estimator charges about 3 sq ft of surface per lineal foot of railing (top rail, balusters, both faces), which is where most stain estimates quietly go short.
How it works
Floor first: length × width. Railings add about 3 sq ft per lineal foot — a 20-ft railing run is 60 sq ft of balusters and rails, roughly a third of a mid-size deck's floor. Coverage per gallon per coat depends on the wood's thirst: 250 sq ft for smooth new boards, 175 for weathered, 150 for rough or bone-dry. Multiply total surface × coats, divide by coverage. Quarts are shown because the difference between 2.88 gallons and 3 gallons is one quart can you do not want to drive back for.
Formula & worked example
Formula: Gallons = (deck area + railing lineal ft × 3 sq ft) × coats ÷ coverage. Coverage per gallon per coat: 250 sq ft new smooth wood, 175 weathered, 150 rough or very dry. Quarts = gallons × 4, rounded up.
Worked example: A 16 × 12 ft deck, 2 coats on weathered wood, 20 ft of railing: 252 sq ft of surface × 2 ÷ 175 = 2.88 gallons — buy 3 gallons.
When to use this
- You are re-staining a weathered deck and guessing gallons at the store.
- Your deck has long railings that other calculators silently ignore.
- You are comparing transparent, semi-transparent and solid stain coverage.
How to use it, step by step
- Measure the deck floor: length × width.
- Pick the wood condition honestly — weathered is the usual case.
- Choose coats: two for new or stripped wood, one for maintenance.
- Measure the railing run and enter its lineal feet.
What the inputs mean
| Input | What it is | Typical values |
|---|---|---|
| Deck size | Floor length × width | 12 × 10 to 20 × 16 typical decks |
| Wood condition | Drives the coverage rate | Smooth 250; weathered 175; rough 150 sq ft/gal |
| Coats | Number of stain coats | 1 maintenance; 2 standard |
| Railing length | Total railing run to stain | 0 for platform decks; 20–60 ft typical |
Another worked example
A small low deck: 12 × 10 ft, one maintenance coat on smooth newer wood, no railings. Surface 120 sq ft × 1 coat ÷ 250 = 0.48 gallons — one gallon can covers it with testing room to spare (2 quarts would do, but the gallon is the shelf reality).
Frequently asked questions
How much stain do I need for a 16 × 12 deck?
Two coats on weathered wood with 20 ft of railing: the 192 sq ft floor plus 60 sq ft of railing is 252 sq ft of surface; × 2 coats ÷ 175 sq ft per gallon = 2.88 gallons — buy 3 gallons (or 2 gallons and 4 quarts if the shelf math favours it). Skipping the railing count would say 2.19 gallons and leave the balusters a different colour.
One coat or two?
Two on new or stripped wood — the first seals, the second evens the colour. One maintenance coat is fine over sound existing stain of the same type. Solid stain over transparent (or the reverse) is a compatibility question for the manufacturer, not this page.
Why does old wood need so much more?
Weathering opens the grain and checks the surface; the wood wicks stain deep instead of holding it at the surface. That is why the planning rate falls from 250 sq ft per gallon on new boards to 175 weathered and 150 on rough, dry wood — experience, not pessimism.
When is the best time to stain?
Wood moisture under about 15%, no rain for 24–48 hours either side, and out of brutal direct sun so the stain soaks rather than flash-drying. New pressure-treated lumber usually waits weeks to months until it dries to that moisture level.
Stain or paint a deck?
Stain — paint films peel under foot traffic and horizontal weather; stain wears thin instead and re-coats without stripping. Solid stain is the middle path: paint-like colour, stain-like behaviour.
💰 Deck due for replacement instead?
If the boards are past saving, the Deck Cost Estimator prices a full new deck — materials and labour by decking type — so you can compare restore vs replace honestly.
How long does deck stain last?
Transparent stains 1–2 years on horizontal surfaces, semi-transparent 2–3, solid 3–5 — UV and foot traffic decide more than brand. Railings (vertical) outlast the floor by about double at every tier.
Can I stain over old stain without stripping?
Over the same type in sound condition, yes after a wash and brighten. Switching types, or over peeling film, requires stripping or sanding — the new coat only bonds as well as the failing layer beneath it.