Paint Calculator
🇳🇿 New Zealand version
A Kiwi weekend repaint turns on one question: how many litres, and in what size tins. This version takes room sizes in metres, assumes 12 square metres per litre as its typical spread rate, and adjusts for texture and colour change before rounding up to whole tins.
Use Paint Calculator online
Paint Calculator
Work out how much paint a job really needs — walls, ceilings and trim, adjusted for texture, colour change and the number of coats — then turn it into a shopping list.
Area to cover, by room
New Zealand rules and figures
- New Zealand rooms are measured in metres and square metres, so the page opens in metres, litres and square metres per litre.
- No official body sets paint coverage in New Zealand, and the 12 m² per litre used here is a typical manufacturer figure.
- Shelf prices in New Zealand already carry GST at 15%, so enter the tin price exactly as it is marked in the shop.
- The starting tin is 2.5 litres, and the cost stays blank until a price is entered.
Sources: Inland Revenue: New Zealand tax authority (GST rate) (checked 2026-11-08)
How the Paint Calculator works
Wall area comes from the perimeter and height, less standard openings. The ceiling uses floor area and woodwork is estimated from skirting, door faces and casings. Litres follow from coats and an effective spread rate, then the tin count rounds up.
litres = m² × coats ÷ effective spread; effective spread = m² per litre ÷ texture ÷ (1 + slider × 0.0035)
- The colour slider starts at 50. That lifts wall and woodwork paint use by 17.5%, which is why the wall figure shows lower than 12 m² per litre.
- Doors count as 0.81 × 2.03 m and windows as 0.9 × 1.2 m for deductions, whatever their real size.
- Woodwork and primer begin at 300 ÷ 350 of the wall figure, which is 10.3 m² per litre.
- Tins start at 2.5 litres, and the price field is empty until you type what a tin costs in dollars.
How to use the Paint Calculator
- Add each room. Type length, width and height in metres for every room, plus how many doors and windows it has.
- Select the surfaces. Tick whether the walls, the ceiling and the trim are in the job, since a spare room may only need walls.
- Set coats and coverage. The Paint needed tab lets you change the coats and the spread rate for each product to match the label.
- Choose a tin and price. Enter the size of the tin you plan to buy and what it costs, in the Container and Price each boxes.
- Export the shopping list. Copy list puts the order in your clipboard for a message, and Export CSV downloads it.
Example: A 3.7 × 3.4 × 2.7 m bedroom, walls only
This bedroom has 1 door and 1 window, which leaves 35.62 m² of wall to cover. The default colour slider of 50 brings the spread rate down to 10.21 m² per litre. At 2 coats, the walls need 6.97 litres, which means 3 tins of 2.5 litres with 0.53 litres left in the last one. Switch on the ceiling box and it adds 12.58 m² of ceiling at 12 m² per litre.
When to use the Paint Calculator
- Weekend repaint of one room. Enter a bedroom, tick the walls and see how many tins to buy before Saturday.
- Weatherboard interior. Add every room, tick the woodwork box where skirting is high, and note the extra gloss volume.
- Rental refresh. Price a quick coat on walls only using the cost of one tin and the number of tins listed.
- Comparing 1 and 4 litre tins. Change the container size to compare the leftover paint across tin sizes.
What the Paint Calculator does not do
- The starting spread rates are typical manufacturer figures, not an official standard, so a tin that states a different rate needs that figure typed into the spread-rate box. Other countries start with litres and no price, which you enter.
- Doors and windows use one standard size each, so a patio door or a large picture window is under- or over-deducted.
- Rooms are rectangles with flat ceilings and no alcoves, stairs, gables or radiators.
- The texture and colour factors are rules of thumb, not a paint maker's data. Check the spread rate printed on your tin.
- Nothing is saved: the rooms reset to the two examples when you reload.
When something else is a better fit
- When you want floor area, perimeter and a boxes-of-material order for flooring, use the Room Measurement Calculator.
- When you need to convert gallons, litres or square measures, use the Unit Converter.
- When the surface is exterior brick, a ceiling with beams or a spray job, use the paint manufacturer's own calculator or a trade quote.
Questions about the Paint Calculator
How many tins does a bedroom need?
The starter 3.7 × 3.4 × 2.7 m bedroom with one door and one window needs 6.97 litres for two wall coats, so 3 tins of 2.5 litres. Larger rooms or darker colours need more.
Does the tool know New Zealand paint coverage?
It uses 12 square metres per litre as a typical figure for the country. No official standard exists, so replace it with the rate printed on the tin you choose.
Why is the wall rate lower than 12?
The colour slider starts at 50 and adds 17.5% to wall paint, so 12 becomes 10.21 m² per litre. Drag it to 0 for a like-for-like repaint in a similar shade.
Can I include the ceiling and skirting?
Yes, tick Paint the ceiling and Paint trim, doors and skirting per room. The ceiling uses floor area and trim uses skirting, door faces and casings, each with its own coats and rate.
Is GST added to the cost?
No. The tool multiplies the tin price you type by the number of tins. New Zealand shelf prices already include 15% GST, so use the price shown in the shop.