2.5 litre or 5 litre tin: which costs less?
The tin that costs less is the one with the lower total for the litres you need, not the one with the lower price per litre. A bigger tin can have a lower price per litre, and you still pay for every litre in it, used or not. This page works out both choices with BuildBatch’s pack optimiser, using example prices that are made up.
How this page was made
Kind of page: Worked example, not tested. Every quantity comes from BuildBatch’s own pack optimiser and paint arithmetic, run on 29 September 2026. The prices are made up: each one is marked “example”, they are not any shop’s prices, and this page names no maker and no shop.
It was drafted with AI tools, and its quantities are checked against the optimiser by an automated test. No tradesperson and no other person has checked it. How BuildBatch compares products says what “worked example” means.
How the optimiser chooses
You give it the litres you need, the tin sizes to choose from and a price for each size. It finds the combination of tins that covers the litres at the lowest total cost. If two combinations cost the same, the one with less left over is chosen, then the one with fewer tins. If any price is left blank it compares the litres left over instead.
It compares only the sizes and prices you enter. It says nothing about other shops or other paints. Three things it does that a price per litre does not:
- It counts whole tins. You cannot buy 1.886 L. You buy 2.5 L.
- It counts what is left over. The paint you do not use is paid for.
- It mixes sizes. For 6.742 L the answer can be one 5 L tin and one 2.5 L tin.
Two example price lists
| Price list | 2.5 L tin | 5 L tin |
|---|---|---|
| List A | £20.00 example£8.00 example a litre | £34.00 example£6.80 example a litre |
| List B | £20.00 example£8.00 example a litre | £42.00 example£8.40 example a litre |
Sources. Price list A and price list B. No maker or shop is a source here. The prices are made up. The tins, totals and litres left over are the output of BuildBatch's pack optimiser, run on 29 September 2026 (how estimates work).
List A prices the 5 L tin below two 2.5 L tins, so it costs less per litre. List B prices it above two 2.5 L tins, to show that the answer can go the other way. Neither is a real price.
The same room, three amounts of paint
The litres come from the paint calculator’s own arithmetic for a room 4 m long, 3 m wide and 2.4 m high, with one door (0.826 m × 1.981 m) and one window (1.2 m × 1.1 m), two coats and 10% extra:
- The ceiling: 12 m² × 2 coats ÷ 14 m² per litre × 1.1 = 1.886 L.
- The walls: 30.644 m² × 2 ÷ 14 × 1.1 = 4.815 L.
- The walls again, at 10 m² per litre, which is where BuildBatch’s own example starts: 30.644 m² × 2 ÷ 10 × 1.1 = 6.742 L.
The 14 m² per litre is an example, not a maker’s figure. Coverage is the number on your tin: see paint coverage explained.
| Litres needed | 2.5 L tins only | 5 L tins only | Lowest total, either size |
|---|---|---|---|
| 1.886 LThe ceiling, at 14 m² per litre | 1 × 2.5 L£20.00 example0.614 L left over | 1 × 5 L£34.00 example3.114 L left over | 1 × 2.5 L£20.00 example0.614 L left over |
| 4.815 LThe walls, at 14 m² per litre | 2 × 2.5 L£40.00 example0.185 L left over | 1 × 5 L£34.00 example0.185 L left over | 1 × 5 L£34.00 example0.185 L left over |
| 6.742 LThe walls, at 10 m² per litre | 3 × 2.5 L£60.00 example0.758 L left over | 2 × 5 L£68.00 example3.258 L left over | 1 × 5 L + 1 × 2.5 L£54.00 example0.758 L left over |
Sources. Price list A, the example room above. No maker or shop is a source here. The prices are made up. The tins, totals and litres left over are the output of BuildBatch's pack optimiser, run on 29 September 2026 (how estimates work).
The ceiling needs 1.886 L. One 2.5 L tin costs £20.00 example and one 5 L tin £34.00 example. The smaller tin costs less, although it costs more per litre, because the 5 L tin leaves 3.114 L unused.
The walls need 4.815 L. One 5 L tin costs £34.00 example and two 2.5 L tins £40.00 example. Both leave 0.185 L over, so here the bigger tin costs less.
At 6.742 L, one 5 L tin and one 2.5 L tin cost £54.00 example, three 2.5 L tins £60.00 example and two 5 L tins £68.00 example. The mix costs least, and no single size does.
| Litres needed | 2.5 L tins only | 5 L tins only | Lowest total, either size |
|---|---|---|---|
| 1.886 LThe ceiling, at 14 m² per litre | 1 × 2.5 L£20.00 example0.614 L left over | 1 × 5 L£42.00 example3.114 L left over | 1 × 2.5 L£20.00 example0.614 L left over |
| 4.815 LThe walls, at 14 m² per litre | 2 × 2.5 L£40.00 example0.185 L left over | 1 × 5 L£42.00 example0.185 L left over | 2 × 2.5 L£40.00 example0.185 L left over |
| 6.742 LThe walls, at 10 m² per litre | 3 × 2.5 L£60.00 example0.758 L left over | 2 × 5 L£84.00 example3.258 L left over | 3 × 2.5 L£60.00 example0.758 L left over |
Sources. Price list B, the same example room. No maker or shop is a source here. The prices are made up. The tins, totals and litres left over are the output of BuildBatch's pack optimiser, run on 29 September 2026 (how estimates work).
With list B the walls (4.815 L) cost £40.00 example as two 2.5 L tins and £42.00 example as one 5 L tin. The smaller tins cost less. In list B the optimiser never buys a 5 L tin: two 2.5 L tins always cost less.
Where the choice switches
The answer changes only when the litres you need pass a multiple of 2.5 L, the point where the tins you had are no longer enough. The prices decide what it changes to.
| Litres you need | List A buys | List B buys |
|---|---|---|
| Up to 2.5 L | 1 × 2.5 L | 1 × 2.5 L |
| Over 2.5 L, up to 5 L | 1 × 5 L | 2 × 2.5 L |
| Over 5 L, up to 7.5 L | 1 × 5 L + 1 × 2.5 L | 3 × 2.5 L |
| Over 7.5 L, up to 10 L | 2 × 5 L | 4 × 2.5 L |
| Over 10 L, up to 12.5 L | 2 × 5 L + 1 × 2.5 L | 5 × 2.5 L |
| Over 12.5 L, up to 15 L | 3 × 5 L | 6 × 2.5 L |
Sources. Price lists A and B, litres from 0 to 15. No maker or shop is a source here. The prices are made up. The tins, totals and litres left over are the output of BuildBatch's pack optimiser, run on 29 September 2026 (how estimates work).
Compare the litres you will use
A price per litre of tin ignores what you leave in the tin. Divide what you pay by the litres you need instead:
- The ceiling, 1.886 L: one 2.5 L tin at £20.00 example is £10.61 example for each litre you use. One 5 L tin at £34.00 example is £18.03 example.
- The walls, 4.815 L: one 5 L tin at £34.00 example is £7.06 example for each litre you use. Two 2.5 L tins at £40.00 example are £8.31 example.
These are worked from the litres before they are rounded to three places. The £10.61 example for the ceiling comes from 1.885714 L. Dividing £20.00 example by the printed 1.886 L gives £10.60 example. The other three figures are the same either way.
The tin’s own price per litre (£8.00 example and £6.80 example in list A) is the same whatever you are painting. The price per litre you use changes with how much of the tin you need.
Leftover paint has a use for touch-ups, which this sum does not value. BuildBatch shows the litres left over, so that you can decide.
What this does not tell you
- Real prices. They differ by shop, colour, offer and date. The sum needs the prices for the paint you are buying.
- Which sizes exist. Not every paint comes in both sizes, or in every colour.
- Different paints. Two paints with different coverage need different litres: see what the tins say.
- Whether you want the leftover. Only you know that.
Do it with BuildBatch
Open the Room Refresh Batch with paint chosen, type the tin sizes and the prices you have been quoted, and it does this sum for you, with a fewer-tins alternative beside it.
Related guides
Questions
Does the bigger tin always cost less?
No. The tin that costs less is the one with the lower total for the litres you need. With the made-up prices on this page, a 2.5 L tin costs less when you need 2.5 L or less, and a 5 L tin can cost less when you need most of it.
Where do the prices on this page come from?
They are made up, and marked "example" each time. They are not any shop's prices, and this page names no maker and no shop. Use the prices you have been quoted for the paint you are buying.