Door paint calculator

Enter the number of doors, the width and height of each door, whether one or both sides will be painted, and the coverage rate printed on the paint label. One coat is assumed unless you request more. The result shows the face area, total paintable area, coated area, exact litres, and a practical quantity rounded up to the next hundredth of a litre.

Measure the doors and choose the painted sides

Begin with the number of doors that share the same dimensions, then measure the width and height of one door. Use the rectangular slab size, not the size of the surrounding frame or rough opening. The calculator multiplies width by height to obtain one flat face, multiplies that area by the door count, and then applies the selected number of sides. Choose one side when only the room-facing surface is being refreshed, or two sides when both faces receive the same coating system. This distinction matters because painting both sides exactly doubles the broad-face area. The estimate deliberately excludes door edges, frames, architraves, glazing bars, raised-panel relief, and hardware. Those details vary too much to infer reliably from height and width alone. If they are part of the job, add a sensible project allowance outside this calculation or measure them separately. Keep width and height in metres when coverage is stated in square metres per litre. If your product uses square feet per gallon, convert all measurements and the final volume consistently before using the result. Group doors by size and run separate estimates when a project contains standard doors, narrow closet doors, and oversized entry doors; then add the paint quantities. This prevents a convenient average size from hiding meaningful differences across a larger schedule.

Apply coats and the manufacturer coverage rate

Coverage rate describes the surface area that one litre can cover for one coat under the manufacturer’s test conditions. Read it from the exact primer, undercoat, enamel, or finish product you plan to use, because different formulations can have noticeably different spread rates. The calculator first finds paintable door area, multiplies it by the number of coats, and divides that coated area by coverage rate. For six doors measuring 0.9 by 2.1 metres, painted on both sides with two coats, the coated area is the single-face area multiplied by six, by two sides, and by two coats. Dividing that figure by ten square metres per litre gives the exact liquid estimate. One coat is the default, but repainting commonly requires two finish coats, and bare material may also need a separate primer calculation using the primer’s own coverage. Do not combine products with different rates into one request. Instead, calculate each layer system separately. Coverage printed on a label is a planning value rather than a guarantee: porous timber, damaged surfaces, deep colour changes, textured panels, application technique, and paint left in rollers or trays can all increase consumption. The exact result is useful for comparison and quoting, while the rounded-up value is a convenient minimum purchase reference. Package sizes still matter, so round further to available tins and retain enough matching paint for touch-ups.

Interpret the result and build a realistic purchase plan

The response separates geometric area from coated area so the estimate can be audited. Area per side is the width multiplied by height. Paintable area includes every selected door face but only once, while coated area includes the coat multiplier. Paint quantity is coated area divided by coverage rate and is rounded to the requested display precision. The additional rounded-up quantity moves the raw requirement to the next hundredth of a litre; it does not pretend that paint is sold in hundredth-litre packages and it does not include an automatic waste percentage. Compare that value with the tin sizes available from your supplier and round up to a purchasable combination. A professional quote may add a separately documented allowance for absorption, overspray, spillage, future maintenance, or intricate profiles. Keeping that allowance outside the core equation makes the output transparent: two estimators using the same door schedule and label coverage receive the same deterministic base quantity. This calculator works best for flush or broadly rectangular doors. Panelled, louvred, carved, or heavily glazed doors may have less or more effective coating area than their simple rectangle suggests. Frames and trim should be estimated independently because their narrow surfaces are usually measured by length and profile rather than door-face area. Run one request per door-size group and per paint product, sum the returned exact quantities, apply your stated contingency, and finally map the total to package sizes. Through the API, each successful deterministic estimate costs $0.002; the browser version uses the same arithmetic for free planning.