Find the four-wall area
For a rectangular room with a uniform wall height, multiply its perimeter by the height. The ceiling is excluded from this example.
2 × (4 + 3) × 2.5 =
35 m²
Paint Calculator
Calculate how much paint you need for a room, individual walls or a known area. Include ceilings if needed, subtract doors and windows, and estimate paint quantities and optional costs.
How to Use the Paint Calculator
Enter your surface measurements, then add the coverage from your paint label and your planned coats. Include tin sizes and prices only if you need a purchase quantity or paint cost estimate.
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Choose your surfaces and enter measurements
Select “Whole room”, “Individual walls” or “Known paintable area”. Choose the measurement or area unit and enter the values requested. Whole room includes all four walls of a rectangular room with a uniform wall height. Include the ceiling only when it uses the same paint and number of coats.
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Subtract doors and windows where needed
Open “Subtract doors and windows (optional)” and enter the dimensions and quantities of openings that will not be painted. Add separate entries for different sizes and count each opening once. In “Known paintable area” mode, enter the net area after deductions; openings are not deducted again.
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Enter paint coverage and number of coats
Use the coverage for one coat stated on your paint label. Match the coverage area and paint units to the label, such as m² per litre or ft² per US gallon. Enter your planned number of coats; the calculator starts at two. Add an optional extra allowance for waste or touch-ups, or leave it at 0%.
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Add optional tin details and calculate
Enter a tin size to round your purchase up to whole tins. Add a price per tin or per selected paint unit and choose the currency if you need costs. A price per tin requires its size. Select “Calculate Paint” to see the estimated paint needed and, when tin details are entered, the whole-tin purchase quantity.
Paint Calculation Example
See how room dimensions, unpainted openings and coats become a paint estimate, then round up to whole tins.
Subtract unpainted openings
The door covers 2 m² and the window covers 2 m². Subtract each opening once from the wall area.
35 − (2 + 2) =
31 m²
Calculate paint for two coats
Multiply the net area by the number of coats, then divide by the coverage for one coat. This example adds no extra allowance.
(31 × 2) ÷ 10 =
6.2 L
Round up to whole tins
Divide the paint needed by the selected tin size and round up to the next whole tin.
6.2 ÷ 2.5 = 2.48 →
3 tins
Purchase quantity: 3 × 2.5 L = 7.5 L.
Estimate the paint purchase cost
Multiply the whole-tin quantity by the example price per tin.
3 × USD 30.00 =
USD 90.00
Paint Calculator: Before You Buy
Use your estimate as a starting point, then check these practical details before ordering paint.
MEASUREMENTS
Measure the surfaces you will paint
Include only walls and ceilings receiving the selected paint and number of coats. Subtract doors and windows that will not be painted, and count each surface once. Divide irregular surfaces into non-overlapping rectangular sections where possible.
For walls with different dimensions, work out the
net area using the
Wall Area Calculator,
then enter it under “Known paintable area”.
COVERAGE
Check the coverage on your paint label
Use the stated coverage for one coat from your chosen product’s label or technical data sheet. Surface texture, absorption and application method can affect actual use. Calculate primer and other paint products separately using their own coverage.
Match the coverage units to the label, such as
m² per litre or ft² per US gallon. US gallons
and Imperial gallons are different volumes.
COATS & TINS
Plan coats and available tin sizes
Choose the number of coats recommended for your product and project. Add an extra allowance for waste or touch-ups if needed. Check available tin sizes before comparing estimated paint use with the quantity you will purchase.
The calculator rounds up using one tin size.
Check the extra paint from this rounding before
adding more spare stock, and ask your supplier
whether combining tin sizes suits your order.
BUDGET
Budget for the complete painting project
Confirm whether your paint price is per tin or per litre or gallon. Add labour, primer, tools, masking supplies, surface preparation, delivery and applicable tax to your project budget. The calculator estimates paint material costs only.
With a tin size entered, the purchase cost includes
whole tins. Without a tin size, a price per litre
or gallon uses the calculated paint requirement.
Selecting a currency does not convert prices.
Frequently Asked Questions
Answers about paint measurements, coverage units and how to interpret your estimate.
How do I enter measurements in feet and inches?
Convert the measurement to decimal feet or use inches for all dimensions. For example, 8 feet 6 inches equals 8.5 feet or 102 inches. Do not enter 8.6 feet for 8 feet 6 inches. Use the selected measurement unit for walls, doors and windows. Changing that unit automatically converts measurements already entered.
Can I calculate an irregular room or sloped wall?
Whole room mode assumes four rectangular walls with the same height. For other layouts, select Individual walls and enter non-overlapping rectangular surfaces. For a triangular or trapezoidal wall, calculate its area separately, combine the surface areas and subtract any unpainted openings. Enter the final net area under Known paintable area. For a trapezoid with parallel vertical sides, its area is the width multiplied by the average of the two heights.
Does the result include the ceiling?
In Whole room mode, the ceiling is included only when you select Include ceiling. This adds room length × room width to the paintable area. Include it only when it uses the same paint, coverage and number of coats as the walls. Otherwise, calculate the ceiling separately. In the other modes, include its area manually if it belongs in the same paint estimate.
Should I subtract doors and windows from a known area?
Known paintable area mode expects a net area: subtract any unpainted openings before entering it. The calculator does not deduct doors and windows again in this mode. Whole room and Individual walls modes can deduct openings entered through their optional fields. Count each opening once, and calculate doors or trim separately if they use a different paint.
What if the paint label uses square feet per gallon?
Select Square feet as the Coverage area unit, then select US gallons or Imperial gallons under Paint unit to match the label. Enter the stated coverage for one coat. Confirm which gallon the product uses: a US liquid gallon is approximately 3.785 litres, while an Imperial gallon is approximately 4.546 litres. You can check these values in the volume conversion tables.
Why is the purchase quantity higher than the paint needed?
When you enter a tin size, the calculator rounds up to enough whole tins of that size. For example, an estimate of 6.2 litres requires three 2.5-litre tins, totalling 7.5 litres. The additional 1.3 litres comes from whole-tin rounding, after any extra allowance has already been included. The calculator does not compare combinations of different tin sizes.
What is the difference between estimated-use cost and purchase cost?
Estimated-use cost applies an entered price per litre or gallon to the paint quantity needed, including any extra allowance. Purchase cost uses the quantity rounded up to whole tins when a tin size is provided. With a price per tin, purchase cost is the whole-tin count multiplied by that price, and a tin size is required. These estimates cover paint only and exclude labour, primer, tools, delivery and tax.
Does changing the currency convert my paint price?
No. Currency selection changes the currency label and formatting without applying an exchange rate. Enter your supplier’s price in the currency you select, then calculate again to update the results.
READY TO PLAN?
Get Your Paint Estimate
Enter your surface measurements, paint coverage and number of coats to estimate the paint needed. Add a tin size and pricing if you also want to plan your purchase quantity and paint cost.
Use the Paint Calculator