Example: a 20 × 12 ft deck floor
The floor covers 240 ft², approximately 22.297 m². Two coats and an illustrative 10% allowance give 240 × 2 × 1.10 = 528 ft² of coverage demand. At an assumed 250 ft² per US gallon, demand is 2.112 gallons, rounded to three gallons by the calculator. This example excludes measured rail and stair surfaces.
Define the surfaces included in the job
List deck boards, stair treads, risers, posts, rails and any other faces receiving the selected finish. Note which sides of each element are included. The deck’s plan length and width describe the floor surface only; multiplying them cannot identify all the exposed surfaces of a railing.
Separate areas that use a different product or colour. A floor coating and a rail finish may have different coverage, container sizes and application instructions. Keeping their quantities distinct is more useful than producing one large gallon total with no explanation of scope.
Choose the product coverage before the allowance
Use the selected stain or coating’s documented coverage for the intended surface and application. The example below uses an assumed rate to show arithmetic; it does not establish consumption for transparent, solid-colour or resurfacing products.
BEHR’s calculator separates wood-stain and floor-coating tasks. Maintain that distinction in your own estimate. Product selection, preparation and application conditions are independent decisions that a material count cannot settle. If a site trial provides a better documented coverage figure, replace the rate openly rather than changing the dimensions.
Apply coats to the right coverage basis
When the stated coverage is for one coat, multiply area by the planned coat count. If the supplied yield instead describes a complete application system, confirm what it already includes. Applying both a complete-system yield and an extra coat multiplier can count the same material twice.
Keep allowance for handling or application loss separate from known extra surfaces. A small unexplained percentage is a poor record of a large staircase or complex rail system. Measure that additional scope where practical, then reserve the allowance for loss that remains uncertain.
Plan purchase units and stock credits
The English deck-stain tool rounds to whole US gallons. For containers sold in litres or other sizes, translate the requirement into the actual package volume and round the purchase appropriately. Keep compatible leftovers as a measured stock credit, subject to their usability.
When the same product covers several areas, total the unrounded requirements before choosing containers. Repeatedly rounding each small stair or landing to a full gallon can overstate the order. Retain a deliberate touch-up reserve separately so the estimate shows what is expected consumption and what is stored material.
Do it in order
- Measure the floor and list separate rail or stair surfaces.
- Record product coverage and whether it is per coat.
- Apply planned coats and one documented loss allowance.
- Combine compatible needs before choosing actual containers.
Planning boundary
The estimate does not select a coating, specify preparation or set an application schedule.
Sources checked
Should I increase deck length to include stairs?
Keep the true floor dimensions. Measure stairs separately or clearly document the separate surface allowance.
Is the same coverage valid for every stain?
No. Use the selected product’s coverage basis and application instructions; the entered rate is not a universal value.