TL;DR
The Dulux paint calculator is free and its real strength is that it knows its own paint: pick a Dulux product and it applies that range's exact coverage and recommended coats, then links you straight to buying it. Pick the Calc Garden paint calculator when you want a brand-neutral estimate for any paint: you type the coverage figure from your own tin, it shows the wall-area formula so you can check the maths, and it needs no account and no product selection. The honest catch is that Dulux does the coverage lookup for you if you are buying Dulux, whereas Calc Garden asks you to read the coverage off the tin yourself.
What the Dulux paint calculator is
Dulux is one of the best known paint brands, and its paint calculator is the front door to its shop. You give it the dimensions of the room, tell it how many windows and doors to subtract, and ideally select a specific Dulux product, and it returns how much paint you need along with a recommended number of coats. Because it is built around Dulux's own product data, it can apply the right coverage rate for the exact finish you are buying, which is genuinely useful if you have already settled on a Dulux range.
The trade-offs are about purpose rather than the arithmetic. The calculator's job is to help you buy Dulux paint, so it is oriented around product selection and shopping, and its coverage assumptions match Dulux products rather than whatever tin you might have in the garage. None of that is hidden or dishonest, but if you are using a different brand, or just want a quick brand-agnostic number, the tool is doing more than you need and quietly assuming one manufacturer's paint.
Where a free, brand-neutral tool helps
A lot of the time you just want the number, and you are not necessarily buying Dulux. You have the room measurements, you know roughly what coverage your paint claims on the tin, and you want to know how many tins to put in the trolley without picking a product first. That is the gap Calc Garden's paint calculator fills: enter the room length, width and height, the number of coats and the coverage per litre, and it shows the litres of paint and the number of 2.5 litre tins to buy, for any brand.
Under the hood it measures the four walls as 2 times length plus width, multiplied by the height, subtracts about 1.8 square metres for each door or window, then multiplies by the number of coats and divides by the coverage per litre. It states that formula on the page so you can check the maths yourself, and it recalculates the instant you change a figure. Everything runs in your browser, so nothing you enter is sent anywhere. Once the walls are sorted, the tile calculator sizes a splashback or floor and the concrete calculator handles a base, so a whole project can be measured in one place.
Dulux paint calculator vs Calc Garden
The two tools answer the same question but from different starting points: Calc Garden gives a clean brand-neutral estimate from a coverage figure you supply, while Dulux ties the estimate to a specific product so it can look the coverage up for you. In the table below a "Yes" means the tool does it cleanly, "Partial" means it does it with caveats, and a dash means it does not. The pricing row reflects each tool as of 2026.
| Capability | Calc Garden | Dulux |
|---|---|---|
| Price (as of 2026) | Free, no signup | Free, no signup |
| Estimates litres from room size and coats | Yes | Yes |
| Works for any paint brand | Yes | Partial |
| Looks up coverage from a chosen product | No | Yes |
| Lets you type the coverage from your own tin | Yes | Partial |
| Shows the wall-area formula on the page | Yes | Partial |
| Converts litres into tins to buy | Yes | Yes |
| No product selection or shop funnel | Yes | No |
| Runs entirely in your browser | Yes | Partial |
| Updates live as you type | Yes | Partial |
Read it honestly. Dulux wins when you are buying Dulux: it knows the coverage and recommended coats for each of its ranges, so you do not have to read the tin, and it removes a step by taking you straight to the product. Calc Garden wins on flexibility and focus: it works the same way for any brand, shows the formula, and asks nothing of you beyond the measurements. This is not an "only free one" claim. Homebase, B&Q and several decorating sites publish free paint calculators too, and some of them, like Dulux, are tied to their own product ranges.
Dulux paint coverage per litre, by product
This is the figure both calculators actually run on, and it is the one thing Dulux's tool looks up for you. The rates below are Dulux's own published "up to" spreading rates, read off the Dulux Trade product pages and the Easycare technical data sheet in July 2026. The litres column applies the paint calculator's formula to a standard 4 m by 3 m room with 2.4 m walls and 2 openings, which is 30 square metres of paintable wall at 2 coats.
| Dulux product | Typical use | Coverage | Litres for a 30 m2 room |
|---|---|---|---|
| Dulux Trade Supermatt | New plaster still drying out | up to 18 m2/L | 3.3 L |
| Dulux Trade High Gloss | Wood and metal trim | up to 18 m2/L | 3.3 L |
| Dulux Trade Vinyl Matt | Interior walls and ceilings | up to 17 m2/L | 3.5 L |
| Dulux Trade Undercoat | Wood and metal, under gloss | up to 17 m2/L | 3.5 L |
| Dulux Trade Satinwood | Wood and metal trim | up to 17 m2/L | 3.5 L |
| Dulux Trade Vinyl Silk | Interior walls and ceilings | up to 16 m2/L | 3.8 L |
| Dulux Trade Vinyl Soft Sheen | Interior walls and ceilings | up to 16 m2/L | 3.8 L |
| Dulux Trade Diamond Matt | Walls in high traffic rooms | up to 16 m2/L | 3.8 L |
| Dulux Trade Diamond Eggshell | Durable wood and metal | up to 16 m2/L | 3.8 L |
| Dulux Trade Weathershield Smooth Masonry | Exterior masonry | up to 16 m2/L | 3.8 L |
| Dulux Easycare Washable & Tough Matt | Retail washable walls | up to 13 m2/L | 4.6 L |
The useful part is the spread. Dulux's own range runs from 18 square metres per litre down to 13, so the thirstiest paint here needs about 38 percent more than the most economical one to cover the same wall. Trade Supermatt goes furthest because it is built to soak into new plaster, while retail Easycare Washable & Tough is the lowest of the group at 13, which is the number that catches people out: it is the Dulux paint most likely to be in a home decorator's trolley, and it is not the 18 square metres per litre a trade product manages.
Two honest caveats. First, these are "up to" figures measured on sound, sealed surfaces, so bare plaster, textured walls and a light colour over a dark one will all come in under them. Second, for one small room the difference often disappears at the till: every product in the table lands this 30 square metre room in two 2.5 litre tins, because tins only come in whole sizes. The coverage rate starts to matter when the job is big enough that the rounding stops hiding it, which is why it is worth reading off your own tin rather than assuming. Dulux itself agrees on that last point: its retail how much paint do you need guide publishes no per-litre figure at all and tells you to divide by "the square metre per litre listed on your paint tin", which is exactly the number Calc Garden's calculator asks you for.
When to pick each one
Reach for Dulux when you have already decided to paint with a Dulux product and want its exact coverage applied for you, or when you want the estimate to flow straight into buying that paint. Those are real conveniences that a brand-neutral tool cannot match, and they are the right call if Dulux is your paint.
Reach for the Calc Garden paint calculator when you are comparing brands, using paint you already own, or just want a quick number without picking a product first. It is also the cleaner choice if you would rather not be funnelled toward one manufacturer's shop while you are still working out how much to buy.
How much paint a room actually needs
Every paint calculator, Dulux and Calc Garden included, starts from the same arithmetic. Measure the perimeter of the room as 2 times length plus width, multiply by the wall height for the total wall area, then subtract roughly 1.8 square metres for each standard door or window you are not painting. Multiply the paintable area by the number of coats and divide by the coverage per litre printed on the tin. The only figure that really moves between tools is that coverage rate, and as the table above shows it swings from 18 square metres per litre to 13across Dulux's own range, before you even look at another brand. That is exactly why typing your own coverage matters.
Whatever produces it, the result is an estimate, not a guaranteed amount. Bare plaster, textured surfaces and a light colour over a dark one all use more paint than the coverage rate assumes, so round up to whole tins and keep one back for touch-ups. For the rest of a decorating project the tile calculator and concrete calculator cover the other materials, and the guides index collects the rest of our explainers, including how much concrete for a shed base and how much soil for a raised bed.