Paint Calculator
Estimate how much paint you need for a room, walls, ceilings or a known surface area. Calculate paint coverage, litres, US gallons and optional cans and cost from the measurements and coverage printed on your paint product.
Paint project
Start with the smallest set of inputs needed for a useful estimate.
Advanced settings: openings, ceiling, waste, cans & cost
How to use, formulas, worked example, FAQs & related paint tools
How to Use the Paint Calculator
Choose Room dimensions when you know the room length, width and wall height. Choose I know the area when you already have a measured paintable surface, which is useful for exterior walls or irregular projects. Enter the number of coats and the coverage rate shown on the paint can, then use Advanced settings for doors, windows, ceilings, waste, can size and cost.
Paint Calculator Formula
For a rectangular room, the gross wall area is the perimeter multiplied by wall height:
Subtract the area of doors and windows, then add a ceiling or other measured painted surfaces when required:
The amount of paint is based on coverage and the number of coats:
When an allowance is used:
Paint Coverage Calculator
Paint coverage is normally stated by the manufacturer for a particular product and surface. ToolVault therefore lets you replace the default planning value with the coverage printed on your paint product. A rough or porous surface, color change, application method and product type can change the actual coverage. Product instructions should take priority over generic rules of thumb.
Wall Paint Calculator and Paint Calculator in Square Feet
For a wall-only job, use Room dimensions for a rectangular room or I know the area when the total wall surface is already measured. Switch to Imperial mode for feet and square feet. The same calculation can be viewed in litres and US gallons so the result is useful across common measurement systems.
Ceiling Paint Calculator
A rectangular ceiling uses length × width for its area. Turn on Include the ceiling when you want ceiling paint included in the same room estimate. Ceiling coverage can differ from wall coverage, so use the appropriate product's stated coverage when accuracy matters.
Worked Example: How Much Paint Do I Need?
Suppose a room is 4 m long, 3 m wide and 2.7 m high, with 2 coats. There are no openings for this example and the ceiling is not included.
Gross wall area = 2 × (4 + 3) × 2.7 = 37.8 m².
With a coverage rate of 10 m²/L per coat, theoretical paint = 37.8 × 2 ÷ 10 = 7.56 L.
With a 5% planning allowance, purchase quantity = 7.56 × 1.05 = 7.938 L, or about 2.10 US gallons.
How Many Gallons of Paint Do I Need?
ToolVault converts litres to US gallons using the standard relationship:
Because paint products are sold in product-specific container sizes, a whole-can result is only shown when you enter the actual can size. This avoids assuming that every “gallon” or tin has the same usable volume.
How Accurate Is a Paint Estimate?
The geometry is deterministic for the dimensions entered. The uncertainty comes mainly from product coverage, surface condition, application method, number of coats and waste. A paint calculator is therefore best treated as a planning and purchasing estimate, not a guarantee of final consumption. Manufacturers also note that actual paint requirements can vary with the selected product and surface.
Frequently Asked Questions
How much paint do I need for a room?
Calculate the paintable wall and ceiling area, multiply by the number of coats and divide by the product's coverage rate. Add any planning allowance only after the geometric and coverage calculation.
How much paint covers 100 square feet?
It depends on the product's coverage. Convert 100 ft² to about 9.2903 m², then divide by the coverage in m²/L and multiply by the number of coats.
Does the calculator subtract doors and windows?
Yes. In Room dimensions mode, enter the combined area of doors, windows and other unpainted openings in Advanced settings and the calculator subtracts it from the wall area.
Does it calculate ceiling paint?
Yes. Turn on Include the ceiling. The ceiling is calculated separately as room length × room width and then included in the net painted surface.
Can I use it for exterior paint?
Yes. Select I know the area and enter the measured exterior paintable surface. This is particularly useful when the exterior walls are irregular or have already been measured.
Why should I use the paint can's coverage rate?
Coverage varies by product and surface. Using the current manufacturer's stated coverage makes the estimate more relevant than applying one universal rule.