Wall Paint Calculator
To calculate wall paint, measure each wall's width and height, multiply width × height to find wall area, subtract doors and windows, then account for the number of coats, paint coverage, surface texture, application method, and spare allowance. The calculator then converts the required paint into gallons or litres and can estimate the number of paint cans or containers required.
The Wall Paint Calculator calculates paint quantity for individual walls or an entire room. Enter the wall width (W) and height (H) using feet, inches, metres, centimetres, or yards, then enter door and window counts when openings need to be deducted. For a whole-room calculation, enter the room length (L), room width (W), wall height (H), and the number of identical rooms. The calculator can separate a main wall colour from an accent colour, apply different coats and paint coverage rates, adjust coverage for wall texture and application method, add a spare paint allowance, and show the result in gallons, litres, square feet, square metres, and square yards. This gives you a practical estimate of paint coverage, paint quantity, wall area, paint cans, paint cost, labour, preparation, and total project cost before buying materials.
Wall Paint Calculator
Your walls
Standard opening sizes
Colours & coats
Cost estimate ($)
How the Wall Paint Calculator Works
The calculator finds the total wall surface area, removes the area covered by doors and windows, and applies paint coverage, coats, surface-loss adjustments, and spare allowance. The result shows the estimated paint volume, containers, coverage area, and optional project cost for the selected wall or room configuration.
Measure the Walls
Enter each wall's width and height, or enter room length, room width, and wall height for a whole-room calculation.
Deduct Openings
Enter door and window quantities and their standard sizes so the calculator removes those areas from the paintable wall surface.
Calculate Paint
Apply coats, spread rate, texture, application method, spare allowance, container size, and optional prices to produce the final estimate.
Wall Paint Calculator Formula
The calculation uses wall dimensions, opening deductions, paint coverage, coats, surface-loss adjustments, and spare allowance. The same measurement principles apply whether dimensions are entered in feet, inches, metres, centimetres, or yards.
Wall Area
For an individual wall, multiply the wall width by the wall height.
Wall Area = Width × HeightWhole-Room Wall Area
For four walls, multiply the room perimeter by the wall height and then multiply by the number of identical rooms.
Gross Area = 2 × (Length + Width) × Height × QuantityDoor & Window Area
Each opening uses its width and height. Door and window areas are multiplied by their respective quantities.
Opening Area = (Door W × Door H × Doors) + (Window W × Window H × Windows)Net Paintable Area
The calculator subtracts opening area from gross wall area and does not allow the result to become negative.
Net Area = Gross Wall Area − Opening AreaEffective Coverage
Texture and application adjustments reduce the selected paint spread rate before the paint volume is calculated.
Effective Coverage = Spread Rate × (1 − Texture Loss − Method Loss)Paint Volume
The required wall area is multiplied by the number of coats and increased by the selected spare allowance.
Litres = (Area × Coats ÷ Effective Coverage) × (1 + Spare %)Paint Containers
When paint is purchased by a container, the required volume is divided by container capacity and rounded up to a whole container.
Containers = Ceiling(Required Litres ÷ Container Litres)Estimated Cost
Optional paint, labour, preparation, and sundries prices can be combined to estimate the total project cost.
Total Cost = Paint Cost + Labour/Prep Cost + SundriesWall Paint Calculator Example
A practical example shows how the measurements move through the calculation. The following example uses wall-by-wall measurements, standard openings, two coats, a selected spread rate, and a spare allowance.
Example Room & Paint Estimate
Sample measurements for a typical room using feet and gallons.
Helpful Information Before Using the Wall Paint Calculator
Measure the Surface Correctly
- Measure width and height: Record each wall's width and floor-to-ceiling height using the same measurement unit.
- Measure openings: Record door and window width and height, then enter the number of doors and windows on each wall.
- Use whole-room mode: Enter room length, room width, wall height, and identical-room quantity when four walls can be represented by the room perimeter.
- Separate accent walls: Assign individual walls to the accent colour when different paint products, coats, coverage rates, or container sizes apply.
- Check unusual surfaces: Use actual wall dimensions for alcoves, partial walls, vaulted ceilings, stair walls, large openings, or irregular layouts rather than relying on a simple rectangular room measurement.
Paint Coverage Factors
- Paint type: Flat, matte, eggshell, satin, semi-gloss, gloss, exterior acrylic, deep-base, and masonry paints can have different spread rates.
- Number of coats: Two coats require approximately twice the coverage volume of one coat before other adjustments.
- Wall texture: Textured, rendered, or masonry surfaces can consume more paint than smooth sealed walls.
- Application method: Roller nap and airless spray settings can change practical paint coverage.
- Spare allowance: A 5% or 10% allowance provides additional paint for touch-ups, variation, and practical project needs.
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Frequently Asked Questions
These answers explain the most important measurement, coverage, quantity, and cost questions related to wall paint calculations.
How do I calculate how much paint I need for a wall?
Multiply the wall width by its height to calculate gross wall area, subtract the area of doors and windows, then divide the net paintable area by the paint's effective coverage and multiply by the number of coats. Add the selected spare allowance to obtain the estimated paint quantity.
How many square feet does one gallon of paint cover?
Paint coverage depends on the product and surface. This Wall Paint Calculator uses the selected spread rate, with examples such as 380 ft² per gallon for eggshell paint and different rates for other finishes. The actual coverage can decrease on textured or difficult surfaces.
Should I subtract doors and windows when calculating wall paint?
Yes. The calculator subtracts the area of the doors and windows entered for each wall. A 3 ft × 6.75 ft door, for example, removes 20.25 ft² from the gross wall area before paint quantity is calculated.
Does the Wall Paint Calculator calculate two coats of paint?
Yes. You can select 1, 2, or 3 coats for the main colour and separately for the accent colour. The paint volume increases according to the selected number of coats.
Can I calculate paint for an accent wall separately?
Yes. Enable the second colour and assign individual walls to the accent colour in wall-by-wall mode. The calculator then calculates main and accent wall areas, spread rates, coats, paint volumes, and containers separately.
Can I calculate paint for an entire room instead of measuring every wall?
Yes. Whole-room mode uses room length, room width, wall height, and the number of identical rooms to calculate the four-wall perimeter area. Doors and windows can then be deducted using their quantities and standard opening sizes.
What measurement units can I use in the calculator?
You can enter dimensions in feet (ft), inches (in), metres (m), centimetres (cm), or yards (yd). The calculator converts the measurements internally so the final wall area and paint quantity remain consistent.
Does the calculator estimate paint cost as well as paint quantity?
Yes. Optional pricing can be entered per can, gallon, litre, square foot, square metre, or square yard. Labour, preparation/filling, and sundries can be added to produce an estimated total project cost and an all-in cost per square foot.