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Quickly estimate how many litres and cans of paint you need based on room dimensions, door and window areas, paint coverage, and number of coats.
Fill in the net size of the room and automatically calculate the area of the four walls
Door and window area will be deducted from the total wall area
Door
Window
Adjust coverage and packaging specifications according to product description
Please enter the length and width of the room to view usage
Overview
Understand what the tool solves, how it works, and the boundaries of its data.
Use this calculator to estimate paint volume for four interior walls, with an optional ceiling. Measurements are metric: room dimensions and opening sizes are in meters, areas are in square meters, paint volume and package capacity are in liters, and coverage is entered as square meters per liter per coat. The result reports paintable area, estimated liters including the waste allowance, whole packages to buy, and purchase volume. The price-per-liter field feeds a displayed cost in yen; when left blank, the current form treats it as zero. This is a simple arithmetic output, not a US store quote.
Coverage means how many square meters one liter covers for one coat. Use the coverage shown for the specific product; the prefilled value is only a starting input, not a universal paint standard. The result uses the chosen package size to round upward, so the purchased volume can exceed the calculated liters.
Guide
Follow the workflow and verify inputs and outputs with practical examples.
Enter the room’s inside dimensions in meters. The wall estimate assumes a rectangular room with four flat walls; measure irregular areas separately before combining any estimates.
For each type, enter width, height, and number of openings. Set the count to zero when none apply. These rectangular opening areas are subtracted from gross wall area, with net wall area floored at zero.
Read the product label for coverage per liter per coat. Enter the planned coat count and any allowance you want to include for waste or touch-ups. Coverage and allowance directly affect the liters estimate.
Enter the container size in liters. Turn on the ceiling option only if it will be painted; its area is length × width. The price field is interpreted as an amount per liter; the displayed cost multiplies it by whole-package purchase volume. A blank field is treated as zero by the current form.
Use cases
See how the tool fits into real work and everyday tasks.
Measure all four dimensions, include the room’s doors and windows, and leave the ceiling option off. Compare the package count with the chosen paint’s labeled coverage before shopping.
Enable the ceiling area for a flat rectangular room, then review the area and liter breakdown. If the ceiling uses a different product or number of coats, run a separate estimate so each calculation uses the right coverage.
For a 5 m by 4 m room with 2.8 m walls, gross wall area is 2 × (5 + 4) × 2.8 = 50.4 m². One 0.9 m × 2 m door and one 1.5 m × 1.5 m window total 4.05 m², leaving 46.35 m² of wall. At 8.6 m²/L per coat for two coats, the theoretical amount is about 10.78 L. A 10% allowance gives about 11.86 L; with 5 L packages, the estimate rounds up to three packages, or 15 L purchased. This example illustrates the arithmetic only; replace its coverage with the label for your paint.
Q&A
Find concise answers to common questions and confusing cases.
The calculator first includes the chosen waste percentage, then rounds required liters up to whole packages. Purchase volume is package count multiplied by package size, so some remainder may be left over.
Run the estimate with the lower and upper labeled coverage values to see how the result changes. Do not assume the default coverage applies to every paint, surface, or application method.
Calculate them separately when their coverage or coat count differs. A single blended coverage input would hide those differences.
Notes
Review scope, result limitations, and important precautions before use.
This estimate models a rectangular room and rectangular doors and windows. It does not measure alcoves, columns, trim, textured surfaces, unusual ceiling shapes, or other features unless you account for them yourself. It also cannot assess surface preparation, paint opacity, application technique, or the product’s actual performance. Use the can label and project conditions to choose coverage and coats, then compare the estimate with your measured site before buying. The optional cost is in yen because of the calculator’s displayed currency and should not be read as a US dollar estimate.
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