Paint Coverage Calculator
Estimate how much paint and how many cans you need for interior or exterior walls, in metric or US units
Wall and project details
Don’t know the wall area? Use the room size
Walls of a rectangular room: 2 × (length + width) × height, in the unit chosen above. Doors and windows are deducted below.
Two coats are the usual recommendation for even color and washability
Two coats are the usual recommendation for even color and washability.
How to use this tool
- Choose m² (Metric) or sq ft (US) and enter the gross wall area.
- Select the wall surface (smooth, lightly textured or raw/porous) and the number of doors and windows to deduct.
- Set the number of coats and the spread rate printed on your paint can, then choose the waste reserve.
- Read the volume in liters or US gallons, the net area, the total area to cover and the number of cans.
Worked example
Take 45 m² of gross wall, 1 door and 2 windows, a smooth wall, 2 coats, a spread rate of 10 m² per liter and a 10% reserve. The openings remove about 1.9 + 2 × 1.4 = 4.7 m², leaving a net area of 40.3 m². Two coats mean 80.6 m² to cover, so 8.06 L, or 8.9 L with the reserve: 3 cans of 3.6 L. If the same walls are raw drywall, the first coat absorbs 35% more, the area to cover grows to 94.7 m² and the volume to 10.4 L – still 3 cans, but with much less leftover. Use the spread rate from your paint's data sheet, and prime raw surfaces first.
Methodology
The calculator turns wall area into liters or US gallons in one chain of steps: gross area minus openings gives the net area; net area multiplied by (an absorption factor for the first coat plus 1 for each further coat) gives the total area to cover; total area divided by the spread rate and multiplied by the waste margin gives the volume. The spread rate is the area one unit of paint covers in a single coat. It is printed on the can or technical data sheet and differs between products, so use the figure for your paint rather than a generic one.
Wall area to cans: a quick lookup for 3.6 L tins
Assumptions for every row: 1 door and 1 window deducted (3.3 m²), 2 coats, a spread rate of 10 m² per liter, a 10% reserve and 3.6 L cans, in metric mode. Volumes are shown with the number of cans in brackets.
| Gross wall | Net area | Smooth wall | Raw drywall |
|---|---|---|---|
| 20 m² | 16.7 m² | 3.7 L (2) | 4.3 L (2) |
| 30 m² | 26.7 m² | 5.9 L (2) | 6.9 L (2) |
| 45 m² | 41.7 m² | 9.2 L (3) | 10.8 L (3) |
| 60 m² | 56.7 m² | 12.5 L (4) | 14.7 L (5) |
| 80 m² | 76.7 m² | 16.9 L (5) | 19.8 L (6) |
| 100 m² | 96.7 m² | 21.3 L (6) | 25.0 L (7) |
How to read it: the raw drywall column adds 35% to the first coat only, so it needs roughly 17.5% more paint overall, not 35%. Watch the 20 m² row: 3.7 L is just over one 3.6 L can, so you still buy two. At 60 m² the surface alone decides between 4 and 5 cans.
Limits: your paint's real spread rate may differ from 10 m² per liter, so check its data sheet. Ceilings, trim and primer are not included, and this is an estimate, so buying one extra small can for touch-ups is sensible.
Painting and prep essentials
A roller kit, a sander and painter’s tape for preparing and painting a room
Bates 19-Piece Professional Paint Roller Kit with Microfiber Sleeves
A 19-piece roller kit with microfiber sleeves, a frame, a tray and brushes, according to the listing.
DEWALT 5-Inch Variable Speed Random Orbit Sander (DWE6423)
A 5-inch variable-speed random orbit sander, according to the listing, for smoothing patched walls before painting.
SmaringRobot Blue Painters Tape (4 Rolls, 88 Yards Total)
Blue painter’s tape, 4 rolls and 88 yards in total, according to the listing, for masking edges and trim.
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Frequently asked questions
How do I work out the wall area of a room? ▼
Add the length and the width of the room, double it and multiply by the wall height: a 4 × 3 m room with 2.5 m walls has 2 × (4 + 3) × 2.5 = 35 m² of wall. The “use the room size” helper under the wall area does this for you. Deduct doors and windows with the fields below, and add the ceiling separately (length × width) only if you are painting it too.
Why do most calculations assume 2 coats of paint? ▼
Manufacturers usually specify two coats on walls: the first coat seals the surface and evens out how much it absorbs, the second gives an even color and the intended film thickness for washability. Covering a dark color, or going from dark to light, can need three, so raise the slider. Choosing one coat roughly halves the volume, but that saving often shows up as patchy color and a second trip to the store.
How much extra paint do textured or raw surfaces need? ▼
The tool adds 20% to the first coat for light texture or roll stucco and 35% for raw drywall or bare masonry. In the 45 m² example, switching to raw drywall raises the area to cover from 83.4 m² to 98.0 m², so about 9.8 L before the margin instead of 8.34 L. These percentages are estimates; real absorption depends on the product and surface. Applying a sealer or primer first is often cheaper than extra topcoat, and you can then select the smooth surface.
Which paint spread rate should I enter? ▼
Use the number on the can or the technical data sheet, given per liter (m²/L) or per US gallon (sq ft/gal) for one coat on a smooth, sealed surface. Many interior wall paints state roughly 350 to 400 sq ft per gallon, or about 8 to 12 m² per liter, but products differ. Enter the rate in the unit shown next to the field. The 10% waste margin covers roller and tray losses and cutting in, not spills or extra rooms, so add those areas to the wall area.