Free · No email · Working shown
Three calculators that show you the arithmetic
Every painting calculator on the internet hides its assumptions. These publish them: the spreading rate, the opening deduction, the tin sizes, the error margin. Change any of them and watch the answer move. Nothing is sent anywhere and nothing asks for your email.
The three
Pick the question you actually have
Paint quantity
Wall area minus openings, spreading rate, coats and a porosity allowance for bare surfaces. Litres per coat, and the tins to buy.
Exterior surface area
Paintable exterior area from your footprint, storeys, wall height and roof pitch — with an honest error margin.
Landlord repaint return
Your suburb’s real median rent from MBIE (Tenancy Services) rental bond data, against a repaint cost, a rent change and a vacancy reduction.
How to use them together
The sensible order
- Estimate the area. If you do not already know your paintable square metres, the surface-area estimator gets you within about 20% from a footprint and a wall height.
- Turn that into litres. The quantity calculator applies the spreading rate, the coats and the porosity allowance, and rounds to tins you can actually buy.
- Check a quote against it. If a quote's product allowance is a long way from your figure, that is a good question to ask, in either direction — far more litres than the calculation suggests may mean textured substrate and a high-build system, and far fewer usually means thin coats.
- If it is a rental, test the case for doing it. The landlord tool is deliberately unflattering: it makes you state what rent change you actually expect, rather than assuming one.
None of them will give you a price, because no official New Zealand source publishes a cost per square metre for painting and inventing one would undermine everything else on this site.
Questions people actually ask
Do I have to give you an email address to use these?
No. There is no gate, no sign-up and no partial result. All three calculators run entirely in your browser, nothing is transmitted, and nothing is stored. If a calculator on another site asks for your email before it shows you a number, the number is the bait.
How accurate are they?
Each one states its own error margin, because they differ a lot. The paint quantity calculator is arithmetic on your inputs, so it is exactly as accurate as your measurements and your assumed spreading rate. The surface-area estimator is a geometric model of a simplified house and is comfortably ±20% on a real one. The landlord tool is arithmetic on a real sourced rent median plus two figures you choose, and its honesty depends entirely on whether those two are realistic.
Why do you show the working?
Because a number you cannot check is just an assertion, and this whole site is built on the opposite of that. Showing the line-by-line arithmetic also means you can spot which assumption is doing the work — usually the spreading rate, or the opening deduction — and change it rather than accepting ours.
Will these tell me what my repaint will cost?
No, and no honest calculator can. There is no official New Zealand dataset for the cost of a trade, so any site that turns your floor area into a dollar figure has invented the rate. What these tools do instead is give you the physical quantities — square metres, litres, tins — so that when you do get a quote you can check whether its quantities are plausible. The full explanation of that data gap is here.
Can I use them on my phone?
Yes. The fields are numeric-keyboard inputs and the layout collapses to one column. They also work with a keyboard alone and with a screen reader — the result and the working are announced when they change.