Deck & Fence Stain / Sealant Coverage Calculator

Work out the coating area, divide by the product’s coverage rate, and multiply by coats.

Deck area is floor L × W plus railings (~+30%), stairs (+10%), posts (+5%). Fence is run L × H, doubled for both sides. Then divide by coverage — ~250–300 sq ft/gal smooth, less on rough wood — and multiply by coats.

Example: a 16 × 12 ft deck with railings ≈ 250 sq ft; two coats of clear (300 sq ft/gal) ≈ 1.7 gal, so buy 2. Always round up and keep extra.

A gallon covers roughly 250–300 sq ft per coat on smooth or previously sealed wood, and much less — around 150–175 sq ft — on rough, weathered, or bare wood.

Coverage also varies by product: clear sealers spread furthest (~300 sq ft/gal smooth), semi and solid stains are thicker (~250). Spraying can use more than brushing.

These are typical published ranges — always check your product’s label.

It depends on the product. Clear sealers are often one coat, semi-transparent one to two, and solid (opaque) usually two.

More coats mean proportionally more product — two coats need about twice the gallons of one. Follow the label: over-applying penetrating stains can leave a sticky finish that never fully cures.

Bare or thirsty wood may drink the first coat almost entirely, so budget for the recoat when buying.

It’s not required, but it’s a good idea for even protection and longer life. Sealing only the visible face leaves the back exposed to moisture, which can cause uneven weathering and warping.

Coating both sides doubles the area and roughly doubles the product — ticking “Both sides” here multiplies the fence area by two.

If budget or access is limited, at least seal the side that takes the most sun and rain.

Rough, weathered, and bare wood is more porous, so it absorbs far more of the first coat — dropping coverage from ~250–300 sq ft/gal down to roughly 150–175.

New pressure-treated lumber, decks stripped to bare wood, and rough-sawn fence boards all fall into this thirstier category. Smooth, sanded, or already-sealed surfaces spread the product much further.

That’s why the calculator asks for wood condition — it can nearly double the gallons required.

Start with the floor area (L × W), then add for the extras with real surface.

Railings and balusters add ~30% because of all the individual spindles. Stairs add ~10% and posts/caps ~5%. So a 200 sq ft floor with railings, stairs, and posts is closer to 290 sq ft of coating area.

Skipping the railings is the most common way people under-buy — don’t leave them out.

Material cost is gallons needed × price per gallon — typically about $30–$55 per gallon for deck stains and sealers.

A mid-size deck needing 2–3 gallons is roughly $80–$165 in product for a DIY job. A larger deck with railings, or a fence coated both sides, needs more. Hired labor is on top.

The calculator rounds up to whole cans and multiplies by your price, so the cost reflects what you’ll actually buy.

They differ in how much they hide the wood and how far they go.

Clear sealers add water protection while showing the natural grain; they spread furthest (~300 sq ft/gal smooth). Semi-transparent adds tint while letting grain show. Solid (opaque) covers like paint, hiding grain and giving the most UV protection, but can peel over time rather than fade.

More pigment generally means better sun protection but a different look. Choose by the look you want and the maintenance you’ll do.