Why add up the litres and not the tins?

Each room's tins are rounded up on their own, so the part-used tin in every room is bought as well. In the worked example the five rooms' wall tins add to 14, but their litres add to about 31, which is 13 tins of 2.5 L. The ceilings go from 7 tins to 5.

Does a project add the paint of my rooms for me?

Yes. Save each room to the same project from the room refresh planner, and Projects adds up the litres of the same paint, with the same coats, coverage, extra and tin size, and rounds to tins once. Estimates saved from the paint calculator are added up too, apart from the room lists.

Can I add up rooms that are different colours?

No. Two colours are two paints, so add the litres of the rooms that share a colour and round each total on its own. BuildBatch cannot see colour, so it is for you to keep apart.

How much paint for a whole house?

Work out each room’s walls and ceiling on their own, add up the litres of every paint that is the same in all of them, and round each total up to whole tins once. For the small house below, at BuildBatch’s generic example figures, the walls need about 31 litres, which is 13 tins of 2.5 L, and the ceilings about 12 litres, which is 5 tins. Rounding room by room instead would buy 14 and 7.

Do it with BuildBatch, room by room

BuildBatch works out one room at a time, and a project adds the rooms up.

Plan the first room in the room refresh planner with paint chosen: its size and height, and its doors and windows. How to measure a room for paint goes through the measuring. The planner gives the room’s whole list, with the preparation and the tools; the paint calculator gives the paint alone.
Under “Save this list”, name the room and save it to a project named for the house. Do the next room and save it to the same project, and so on round the house.
Open the project in Projects. Under “Added up across the rooms” it adds the litres of the same paint, with the same coats, coverage, extra and tin size, and rounds to tins once: one line for the walls’ paint and one for the ceilings’.

Keep the coats, coverage, extra and tin size the same in every room, or the project keeps them apart. BuildBatch cannot see colour, so add up only the rooms that share one paint.

Worked example: a small house

Five rooms, each 2.4 m high, with the walls and the ceiling painted, on surfaces that were painted before and are sound. Doors and windows are taken off the walls at the planner’s typical sizes, which are not yours: measure your own (what to take off). They are an internal door 762 × 1981 mm, a front door 813 × 2032 mm and a window 900 × 1200 mm. The hall’s three doors are the front door and two internal doors; the landing’s three are internal.

Every figure is BuildBatch’s generic example: 2 coats, 10 m² per litre, 10% extra and 2.5 L tins. They are not the figures of any paint. Each row is one room planned on its own.

Room	Walls	Wall paint needed	Wall tins	Ceiling	Ceiling paint needed	Ceiling tins
Main bedroom (4 × 3.5 m; 1 door, 1 window)	33.41 m²	7.35 L	3	14 m²	3.08 L	2
Second bedroom (3.5 × 3 m; 1 door, 1 window)	28.61 m²	6.294 L	3	10.5 m²	2.31 L	1
Living room (4.5 × 4 m; 1 door, 2 windows)	37.13 m²	8.169 L	4	18 m²	3.96 L	2
Hall (3.6 × 1.8 m; 3 doors)	21.25 m²	4.675 L	2	6.48 m²	1.426 L	1
Landing (3 × 2 m; 3 doors)	19.47 m²	4.284 L	2	6 m²	1.32 L	1
The rooms’ tins added			14			7
The litres added, then rounded once		30.772 L	13		12.096 L	5

Added first, the litres need one wall tin and two ceiling tins fewer than the rooms do on their own. The last tin in each room is part used, and across the house those part tins are shared. That holds only if every room gets the same paint and colour: two colours are two sums.

What the coverage on the tin does

The coverage printed on the tin moves the total more than anything else. The same five rooms at two other example coverages, with everything else unchanged:

Coverage	Wall paint, five rooms	Ceiling paint, five rooms
10 m² per litre (BuildBatch’s generic example)	30.772 L, 13 tins	12.096 L, 5 tins
12 m² per litre	25.643 L, 11 tins	10.08 L, 5 tins
14 m² per litre	21.98 L, 9 tins	8.64 L, 4 tins

The 12 and the 14 are examples too. The figure on your own tin replaces all three.

What else changes the answer

Coats. BuildBatch starts at 2. A third coat adds about half as much again to every room, and the tin says how many it wants: see how many coats of paint do I need?
New plaster. Bare plaster needs a mist coat or a primer-sealer first, which is a separate product and a separate tin: see painting new plaster.
A colour change. A strong change, dark to light, may need an extra coat. Enter the coats you will apply, not the starting 2.
Ceilings in a different paint. Add the ceilings’ litres on their own, as the table does. If one paint goes on walls and ceilings and its tin says it suits both, you can add all the litres together; BuildBatch keeps them apart and does not do that sum.
Woodwork. Skirting, doors and frames are not in these figures. They take their own paint.

What this guide does not cover

Primer, undercoat or mist coat quantities, which come from their own tins. Woodwork. Exterior and masonry paint. Stairwells, where the wall runs up past the landing and needs proper access equipment. The landing here is a flat room 2.4 m high. Choosing a paint or a colour, or whether a paint suits a bathroom or kitchen. Check first with the tin, and with your merchant if you are unsure.