Wall Paint Calculator: How Many Litres Do You Need?
Calculate how many litres of wall paint a room needs, with a 5% allowance for touch-ups and an optional material cost estimate.
For a room measuring 3.5 m by 4 m with 2.5 m ceilings, two coats of interior paint with a yield of 12 m²/L need about 6.6 litres (6.56 L before rounding), including a 5% allowance for touch-ups. A 4 m by 5 m room under the same conditions needs about 7.9 litres. The yield printed on the tin and the number of coats are the two inputs that change the final quantity the most.
The method is straightforward. Multiply the total wall area by the number of coats and by 1.05 for the touch-up allowance, then divide by the paint's yield in square metres per litre. The yield on the tin is a theoretical value for one coat on a sealed, smooth surface under ideal conditions. On site, porous plaster or textured walls absorb more paint, so the real coverage is often lower than the label suggests. Yields also vary between product ranges, so always use the figure printed on the tin you are buying.
The example above uses the full wall area for a 3.5 m by 4 m room, which is 2 × (3.5 + 4) × 2.5 = 37.5 m². Two coats cover 75 m², and dividing by 12 m²/L gives 6.25 L, which rises to 6.56 L with the margin. In practice, that means buying a 5 L tin and a 2 L tin, which gives 7 L and leaves a small reserve for touch-ups. Enter the length, width and ceiling height of each room, then choose the number of coats and the yield, and the calculator returns the litres needed with a suggested pack size.
Most homes in Singapore are HDB flats, condominiums or landed houses, and room sizes vary a lot between them. A four-room HDB flat in Tampines, a condominium unit in Bukit Timah, a landed house in Bishan and a new BTO flat in Punggol can each have very different wall areas, so measure each room rather than estimating from the floor plan.
Run the numbers before you go to the shop, and bring the room measurements and the yield with you. For larger volumes, ask a paint supplier for a quote, and state the number of coats and whether surface preparation is included. Treat the calculated quantity as your target rather than a guess, and enter the price per litre to see an estimate of material cost.
The result updates automatically.
Check the paint tin. Typical values: 10–14 m²/L (about 108–151 sq ft/L).
Litres needed
for an area of 40.0 with 2 coats
- Total area to paint
- 40.0 m²
- Safety margin
- 5% included for touch-ups
How it works
Formula
How the calculation works
How to work out the paint a room needs
Working out the right amount of paint is simpler than it looks, but three variables are usually estimated badly: the real wall area, the yield printed on the tin and the number of coats. This calculator covers all three and adds a 5% allowance for touch-ups, which is a planning margin rather than a fixed rule.
The calculator gives you a quantity to buy. It does not inspect the wall, the condition of the existing paint or the conditions in the room. Treat the result as a planning figure and check it against the product's technical data sheet before you buy. It is least reliable for very porous or heavily textured surfaces, and for specialist finishes such as metallic or lime-based paints, whose coverage may differ from the figures used here.
Calculating the wall area
The area of a rectangular wall is its length multiplied by its height. A square room measuring 4 m by 4 m with 2.5 m ceilings has four walls with a combined area of 4 × 4 × 2.5 = 40 m². Measure from the floor to the ceiling where each wall meets it, and do not forget alcoves and recesses, which add area. The calculator accepts up to 20 walls, so an irregular room can be entered wall by wall rather than estimated as a single rectangle.
Small rooms rarely need doors and windows deducted. The difference is normally covered by the paint lost during the job, such as paint left in the tray, drips and spatter, and the paint used for touch-ups. In larger spaces, or where doors are unusually large, deduct the openings before you enter the total. To do so, measure the width and height of each door and window, work out their areas and subtract the total from the wall area.
The paint yield, where most people go wrong
Yield is the relationship between paint used and area covered, expressed in square metres per litre (m²/L). It is always printed on the tin, usually in small type on the side label. The figure is a theoretical value for one coat on a surface that is already prepared and sealed. Under real conditions, porous plaster, textured finishes and freshly plastered walls absorb more paint, so the coverage you achieve is often lower than the label suggests. For that reason, plan for slightly more paint than the calculation gives.
Yields also depend on the product. Lower-priced paints sometimes state a yield that is hard to achieve on a real wall, so it is worth testing coverage on a spare board or a hidden area before committing to a large batch. Always enter the figure from the tin you are buying, not a figure from memory or from another product.
Water-based paints for interior walls and ceilings are described in the European standard EN 13300, which sets out classification and performance requirements. The product's technical data sheet should state how it relates to that standard. Local authorities may apply additional requirements for particular applications, so check the data sheet and any building or landlord rules that apply to your property before you start.
How many coats do you really need?
- One coat: only for touch-ups over the same colour.
- Two coats: the standard for most jobs. It covers the majority of light-on-light situations.
- Three coats: when moving from a dark colour to a light one, or when the product has low hiding power and two coats leave the old colour showing through.
- Primer plus two coats: new plaster, repaired cracks or a dramatic change of colour.
Skipping a coat to save paint usually leaves an uneven finish, which shows most under side lighting. Allow each coat to dry fully before the next, and apply them in the same direction for the most even result. Remember that the number of coats you enter multiplies the wall area, so a three-coat job needs a proportionally larger quantity.
Worked example: a lower yield and an extra coat
Take the same 3.5 m by 4 m room with 2.5 m ceilings, but use a paint with a yield of 10 m²/L and apply three coats. The wall area is 37.5 m², so the calculation is 37.5 × 3 × 1,05 ÷ 10 = 11.8 L (11.81 L before rounding). The same room with two coats of a 12 m²/L paint needs 6.56 L, so the change in inputs increases the quantity by 80%. The number of coats multiplies the result and the yield divides it, so when you compare two products, use the yield printed on each tin rather than assuming they are similar.
Why the 5% allowance?
The calculator adds 5% to the total because paint never all reaches the wall. Some stays in the tray, some is lost to spatter and drips, and some will be needed later for corners, accidental marks and areas that are hard to cover. The margin protects you from a second trip to the shop halfway through the job.
That matters because a later batch of the same colour can vary slightly. Two batches side by side can show a visible difference, especially in good light. Keeping a small reserve from the same tin is the most reliable way to fix marks later without a colour mismatch.
Paint ranges and finishes for Singapore homes
Interior paints generally fall into three ranges: economy, mid-range and premium. Economy products are widely available at large DIY retailers and smaller shops, and usually have the simplest specification. Mid-range products offer better coverage and a more durable finish. Premium products are often formulated for specific surfaces or longer-lasting performance, and their stated yields can be higher. Compare the yield on the tin alongside the price, because the cheapest tin per litre is not always the cheapest per square metre.
Finish matters too. Matt finishes hide small wall imperfections well, while satin finishes are easier to wipe clean, which is why they are common in kitchens and corridors. In Singapore's humid climate, mould-resistant finishes are worth considering for bathrooms, kitchens and rooms with limited ventilation. The product's data sheet will say which finishes suit which rooms.
Common mistakes to avoid
- Buying a very large tin for a small room. Opened paint loses quality over time, so a 5 L tin is usually a better choice than a 15 L tin for a single bedroom.
- Mixing batches of the same colour. Even a white can vary between production runs. If you need more paint partway through, take a sample of what you already have to the shop.
- Trusting the yield without reading the label. The printed figure is a best-case estimate. Check it on the tin you are buying, and test a patch if the product is unfamiliar.
- Forgetting primer on new walls. Without primer, paint soaks in unevenly and the finish can look blotchy, which often means an extra coat is needed.
Getting advice for a specific situation
If your wall has damp, flaking paint or cracks, the surface needs treatment before painting, and the quantity you calculate will not help until that is sorted. Ask the staff at the paint counter, who can recommend a product suited to the surface. For work that goes beyond decoration, such as repairs to plaster or walls, consult a qualified contractor.
Use this calculator to set the quantity, then confirm the product, the number of coats and the surface preparation before you buy.
Frequently asked questions
How many litres of paint do I need for a bedroom?
A typical bedroom measuring 3.5 m by 4 m with 2.5 m ceilings has about 37.5 m² of wall area before any deduction for doors and windows. With two coats of paint at a yield of 12 m²/L, you need about 6.6 litres. In practice, a 5 L tin and a 2 L tin cover that, with a small reserve for touch-ups. Measure your own room, because bedrooms in HDB flats and condominiums can differ quite a lot in size and ceiling height.
Should I deduct windows and doors from the wall area?
In small rooms you can usually ignore doors and windows, because the paint lost to waste during the job covers the openings. In larger rooms, or where doors are very large, such as in a shophouse unit or a hallway with a wide entrance, deduct them. Measure each door and window, subtract their total area from the wall area, and enter the result.
How do I estimate the cost of painting a room in Singapore?
The cost depends on the paint range, the number of coats, the surface preparation and whether you paint yourself or hire a professional. To estimate the material cost, enter the price per litre of the paint you plan to use in the price field of this calculator, and the total appears automatically. If you hire a painter, ask for a written quote that states the paint product, the number of coats and whether surface preparation is included, so that you can compare like with like.
What does paint yield mean?
Yield is the area that one litre of paint covers in a single coat on a well-prepared surface. It is printed on the tin in square metres per litre (m²/L). A higher figure means fewer litres for the same wall, but yields on cheaper products are sometimes hard to achieve in practice. A test patch on a spare board or an inconspicuous area will show you how much paint a coat really uses, which is more reliable than the figure on the label alone.
Can I use this calculator for ceilings?
Yes, with a small adjustment. Enter the room's length and width as a single surface, so the area is length multiplied by width, and choose the number of coats you plan to apply. Ceiling paint often has a slightly lower yield than wall paint, so check the figure on the tin before you enter it.
How many coats do I need when changing from a dark colour to a light one?
Typically three coats, or a primer followed by two coats of the final colour. Painting a light colour straight over navy or red with only two coats usually leaves uneven coverage, with the old colour showing through. If you change colour often, a primer with good hiding power is worth using, because it reduces the number of finishing coats. Set the number of coats in the calculator to match, because the result multiplies the wall area by that number.
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By RivoCalc · Reviewed under our editorial methodology · Updated 4 May 2026
The results are estimates. Actual paint use depends on the surface, its porosity, the application method and the real coverage of the product, so check the technical data sheet of the paint you buy and keep a little spare for touch-ups.