Paint quantity calculator
Painting 48 m² of wall with 2 coats at 10 m² per litre takes 9.6 litres, so you buy 10. Enter the wall area or the room's length, width and height, subtract doors and windows, and see what to buy. Free in your browser.
- Free
- Runs in your browser
- No sign-up
- Your data stays on your device
Run — free
Worked example
- Area
- 48
- Number of paint coats
- 2
- Manufacturer coverage
- 10
- Calculation mode
- area
- Gross area
- 48
- Openings
- 0
- Net area
- 48
This paint quantity calculator turns wall area or simple room dimensions into the litres of paint you should buy for a given number of coats and a manufacturer coverage rate. Homeowners, landlords, and contractors routinely under-order by forgetting second coats or over-order when they ignore doors and windows; the arithmetic itself is small but easy to get wrong under time pressure. The engine accepts either a total paintable surface in square metres or length, width, and height so it can form four-wall area as two times the sum of length and width times height. Optional openings subtract door and window voids so you do not paint glass. Coverage is the spread rate printed on the tin in square metres per litre, and coats multiplies the surface once for each layer.
What the calculator returns and how paint volume is defined
Paint volume here is the liquid volume required to cover a net surface area for a stated number of coats at a stated coverage. Coverage is the manufacturer figure for how many square metres one litre covers in a single coat under ideal conditions; real walls, porous plaster, dark colours, and heavy texture often need more product than the tin claims, so treat the result as a planning estimate and round up for safety.
The calculator multiplies net area by coats and divides by coverage, which is exactly the identity used on product data sheets: litres equals area times coats over m² per litre. When you supply room dimensions instead of area, gross wall area is two times the sum of length and width times height, counting the four vertical walls of a rectangular room and ignoring the floor and ceiling unless you add those surfaces yourself via the area path.
Optional openings remove the combined area of doors, windows, built-in cabinets, or other surfaces you will not paint, and the engine rejects a request if openings cancel or exceed the gross wall area so you never get a zero or negative tin count.
Where paint estimates fit for DIY, quotes, and software
DIY painters meet this problem when a weekend project needs a second coat on accent walls, when a landlord budgets a full flat refresh, or when a colour change from dark to light needs more product than a same-family touch-up. Trade estimators use the same identity across dozens of rooms: measure or take dimensions, subtract openings from a schedule, apply the can’s coverage, multiply by coats, and buy whole tins.
Teachers and vocational trainers can pre-generate answer keys for modest room sizes without trusting opaque mobile apps that switch units mid-form or forget that coverage is per coat. Developers call the same contract from scripts to seed deterministic test vectors for renovation calculators, to normalise user-entered room sizes before a cart suggests tin counts, or to satisfy programming-challenge statements that demand litres rather than a hand-waved “about two cans.”
Product tools use the rewrite when a homeowner types five by four by two point four metres and the UI must show net wall area and a clean litre total before checkout.
What you can do with it
Weekend room repaint
Enter length, width, and height with two coats and the tin’s m²/L rating to know how many litres to buy before you start.
Contractor multi-room quotes
Feed known wall areas and openings from a take-off sheet to produce reproducible litre totals for bids and purchase orders.
FAQ
What does the paint quantity calculator cost?
It is free in your browser on this page.
What if I enter zero or negative coats or coverage?
Area, room edges, coats, and coverage must all be strictly positive.
Does this include the ceiling or floor?
Room mode counts four walls only. To include a ceiling or floor, add that surface into area yourself or run a separate estimate and sum the litres.
How do I work out paint for a room from its dimensions?
Enter the room's length, width and height instead of an area. The calculator adds the four walls as twice the sum of length and width, multiplied by height, then subtracts the doors and windows you enter. If those openings equal or exceed the walls, it refuses the calculation.
Why might I need more paint than the result?
The coverage on the tin assumes ideal conditions. Porous plaster, dark colours, heavy texture and a change from a dark colour to a light one often need more product, so treat the result as a planning estimate and round up.
Related tools
For developers — API access
Everything on this page is available programmatically. This section is for teams who want to wire it into their own systems; everyone else can just use the tool above.
API endpoint
Prefer to automate it? One authenticated POST creates the task; the result comes back by webhook or a signed link. The same capability also runs here on the web, by email and from Telegram — and soon from our app too.
Call it from your stack
curl -X POST https://api.kit.forhosting.com/home/paint-needed \
-H "Authorization: Bearer $KIT_KEY" \
-H "Content-Type: application/json" \
-d '{"coats":2,"coverage":10,"area":48}'const res = await fetch("https://api.kit.forhosting.com/home/paint-needed", {
method: "POST",
headers: {
"Authorization": `Bearer ${process.env.KIT_KEY}`,
"Content-Type": "application/json"
},
body: JSON.stringify({
"coats": 2,
"coverage": 10,
"area": 48
})
});
const { task_id } = await res.json();import os, requests
res = requests.post(
"https://api.kit.forhosting.com/home/paint-needed",
headers={"Authorization": f"Bearer {os.environ['KIT_KEY']}"},
json={
"coats": 2,
"coverage": 10,
"area": 48
},
)
task_id = res.json()["task_id"]<?php
$res = file_get_contents("https://api.kit.forhosting.com/home/paint-needed", false, stream_context_create([
"http" => [
"method" => "POST",
"header" => "Authorization: Bearer " . getenv("KIT_KEY") . "\r\nContent-Type: application/json",
"content" => '{"coats":2,"coverage":10,"area":48}',
],
]));
$task = json_decode($res, true);body := bytes.NewBufferString(`{"coats":2,"coverage":10,"area":48}`)
req, _ := http.NewRequest("POST", "https://api.kit.forhosting.com/home/paint-needed", body)
req.Header.Set("Authorization", "Bearer "+os.Getenv("KIT_KEY"))
req.Header.Set("Content-Type", "application/json")
res, _ := http.DefaultClient.Do(req)Example request
{
"coats": 2,
"coverage": 10,
"area": 48
}Example response
{
"task_id": "tsk_a1b2c3d4e5f6a1b2c3d4e5f6",
"type": "home.paint_needed",
"status": "queued",
"_links": {
"result": "/tasks/tsk_…/result"
}
}The API is asynchronous: the call returns a task_id immediately and the result arrives by webhook. Polling is capped at 1 req/s per task.
Pricing
Published price — no tokens, no invented credits. A failed task is never charged.
Limits
max_abs | 1000000000 |
Errors
| HTTP | Code | Meaning |
|---|---|---|
401 | unauthorized | Missing or invalid API key. |
402 | insufficient_balance | Your balance doesn't cover the task price. |
404 | unknown_type | That task type doesn't exist. |
429 | rate_limited | Too many requests. Use the webhook instead of polling. |
Technical notes
The response returns gross and net area, exact litres, and a whole-litre ceiling for shopping, with no network calls and fully deterministic floating-point math.
What the calculator returns and how paint volume is defined
The JSON response echoes mode (area or room), the dimensions when used, gross_area, openings, net_area, coats, coverage, liters to the requested precision, liters_ceil as the smallest whole litre that still covers the exact need, unit tags m2 and L, the method tag, and a short formula string. There is no brand database, no gallon conversion, and no shopping cart: the page answers only the volume question with stable numbers suitable for worksheets, contractor quotes, and API consumers that must match goldens run after run.
How inputs are read, validated, and kept reproducible
Every numeric field must be finite; non-positive area, coats, coverage, or any room edge is rejected, and openings must be zero or positive. Preferred fields are area for a known surface, or length, width, and height for a rectangular room, plus required coats and coverage. Aliases such as wall_area, surface, and sqm for area, l, w, and h for dimensions, layers for coats, and spread_rate or m2_per_liter for coverage are accepted so spreadsheets, query strings, and typed forms can reuse the same contract without renaming columns. You must choose one surface path: either area alone or the full length-width-height triple; mixing both fails with invalid_input so a stale form field cannot silently double-count. An optional precision field, with aliases decimals and dp, chooses how many decimal places to expose for areas and litres, defaulting to four and capped at fifteen so JSON goldens stay stable across engines. Pair the free browser run on this page with the priced API when you need the identical mathematical result inside an automated pipeline without re-implementing the paint formula yourself.
Where paint estimates fit for DIY, quotes, and software
On this page the work runs entirely in your browser; through the API each successful lookup costs $0.002, failed validation is not charged, and nothing is stored after the response returns. That split — free interactive exploration and a priced, identical API — matches the rest of the KIT tier-A catalog and lets you move from a hallway demo to an automated quoting pipeline without changing the mathematical result. Pair it with unit converters when your tape measure is in feet, and with other home or geometry endpoints when you are building a small lab of free, deterministic planning helpers for interiors.
Integration use cases
Deterministic fixtures for apps
Generate stable liters and liters_ceil values for unit tests in renovation planners, e-commerce tin suggesters, and CI checks.
Technical questions
How is paint volume calculated?
liters = (net_area × coats) / coverage, where net_area is either the area you supply or 2×(length+width)×height minus optional openings.
What is liters_ceil?
It is the exact litre need rounded up to the next whole litre, so you can map the result onto whole cans when the store does not sell fractional tins.