Deck Stain & Sealer Calculator

How much deck stain or sealer do you need, and how much should you buy? Include the surfaces you plan to coat and compare your product’s coverage range.

Deck floor

Deck length (ft)

Deck width (ft)

Railings (optional)

Include railings?

If you know the actual railing stainable area, leave this estimator off and enter that area under Other area.

Stairs (optional)

Include stairs?

Other stainable area

Fascia / skirting / posts / benches / other area (sq ft)

Add measured stainable surfaces not already counted. For help, use the Square Footage Calculator below.

Coats

Number of coats

Coats are applied once through total coating area.

Your product coverage

Look on the stain or sealer container/product sheet for coverage in square feet per gallon. If the manufacturer provides a range, enter both ends. For one coverage number, enter the same value for Low and High.

150–250 sq ft/gal is an editable example, not a universal coverage rate. Replace it with your selected product’s label coverage.

Low coverage (sq ft / US gal)

High coverage (sq ft / US gal)

Wood condition / planning assumption

For planning, this option uses the lower, middle or upper end of the coverage range you entered. It does not measure your wood’s absorption.

Deck age alone does not determine stain usage. Older, weathered, rough or very dry wood often absorbs more product, so planning toward the lower end of the product’s stated coverage range may be appropriate.

Allowance and purchase

Waste / extra allowance (%)

Zero is allowed. Added once after accounting for all surfaces and coats.

Container size

Price per container ($)

Optional; purchase cost uses whole containers.

Your deck stain estimate

containers to buy

gal planning quantity including allowance

Selected planning coverage: sq ft / gal
Base stain / sealer before allowance: gal
Exact containers required: containers
Purchased capacity: gal
Estimated unused capacity after allowance: gal

Whole-container purchases use unrounded quantities. Unused capacity is purchased volume minus the requirement including allowance, not a prediction of recoverable leftover product.

Coverage scenarios

Each scenario uses your entered coverage range, the same surfaces/coats and the same allowance. These are planning points, not measurements of absorption.

Porous / low end

Average / midpoint

Smooth / high end

Planning points within your entered product coverage range (sq ft / US gal).

Coverage and whole-container purchases, including allowance
Planning assumption	Coverage (sq ft/gal)	Gallons	Containers to buy
Smooth / upper-end planning
Average / midpoint planning
Very dry / porous / lower-end planning

Project area breakdown

Deck floor: sq ft
Estimated railings: sq ft
Stair treads: sq ft
Stair riser faces: sq ft
Stairs subtotal: sq ft
Other surfaces: sq ft
Total physical surface: sq ft
Number of coats
Total coating area: sq ft

Project and shopping summary

Results are rounded for readability; totals and purchase rounding use unrounded values.

How the estimate works

Add floor area, estimated railing surfaces, stair tread/riser faces and other area. Multiply this physical area by coats once. Divide total coating area by selected planning coverage, add the allowance once, then round up to whole containers.

Understanding coverage and condition

The product label takes precedence. The condition selector chooses a point in the range you enter; it does not add a separate old-deck multiplier or predict absorption. Equal Low and High coverage gives the same result for all three scenarios. If coat-specific label coverage differs, calculate those coats separately rather than assuming one rate describes both.

Understanding the estimate

Actual coverage can vary with wood species, porosity, age/weathering, roughness, sanding/preparation, existing stain/sealer, moisture, application method, product formulation, overspray/drips and railing geometry. Railing factors are example planning estimates, not measured surface areas. Count only the surfaces you plan to coat and avoid overlaps.

This is a purchasing estimate. It does not prescribe stain chemistry, oil vs water, solid vs semi-transparent, preparation method or number of coats. Enter coats from the selected product instructions/project plan and follow the label.

Related: Square Footage Calculator for measured other surfaces, and Deck Board Calculator for a separate decking-material project.