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Deck Stain Calculator

A deck stain calculator works out how many gallons of stain or sealer your deck needs, from its area, the product's coverage rate and how many coats. It factors in railings and steps, which add a surprising amount of surface.

Your measurements

Result

Decking drinks stain — rough or weathered boards and the first coat take much more than the can claims — so this lets you set a realistic coverage and rounds up, because running out halfway across leaves a visible lap line.

How it is calculated

Gallons = deck area × coats ÷ coverage per gallon, with railings/steps added as a percentage of the floor area. Coverage depends heavily on wood condition and product: semi-transparent stains commonly cover 150-250 sq ft per gallon on decking, less on rough or thirsty timber. Round up.

Steps

Enter the deck length and width, or the area.
Set the coverage per gallon (semi-transparent often ~200 sq ft, less on rough wood).
Enter the number of coats.
Add a percentage for railings and steps.
Read the gallons to buy — round up.

Worked example

A 20 × 15 ft deck (300 sq ft) plus 15% for railings, at 200 sq ft/gallon and 2 coats, needs about 4 gallons.

Common questions

How much deck stain do I need?

Deck area × coats ÷ coverage per gallon. A 300 sq ft deck at 2 coats is about 3-4 gallons. The calculator adds railings.

Why does deck stain cover less than the label says?

Decking is rough and porous, and the first coat soaks in. Real coverage is often well below the can's smooth-surface figure.

One coat or two?

Follow the product — many penetrating stains are one coat, film-forming stains two. The calculator handles either.

Do I count the railings?

Yes — railings, balusters and steps add a lot of surface. The calculator adds a percentage for them.