A room-by-room estimate can leave you shopping for several separate projects when the same paint will cover all of them. Start with one supply list for each product, color and finish. Add the work together, subtract the usable paint you have once, then compare whole tins.
The Multi-room Paint Shopping spreadsheet keeps ten rooms in one file. Its useful distinction is between paint needed for the job and paint you still need to buy.
Give each paint its own inventory
Write down the product, color, finish and usable quantity remaining. A label saying “5 L” describes the original tin, not what is left inside. Record the amount available for this project. If you are reserving some for another room or later touch-ups, keep that reserve out of available stock.
Do not pool two different paints because their color names sound similar. The spreadsheet uses one coverage rate and coat count across its rooms. If either varies, keep separate plans; do not average the rates. Dulux notes that coverage and required coats depend on the product and surface. Use the instructions for the paint you are actually buying. Dulux paint calculator guidance.
This inventory does not establish whether an old paint is still usable. Resolve that before counting it. Keep the product details with your saved file so you can check the plan against the tin at the shop.
Work through the rooms before the tins
For rectangular rooms, wall area is perimeter × height. Deduct only the door and window areas you will not paint with this product. The manufacturer’s basic estimating method is to calculate the area, account for coats and divide by the stated coverage. Dulux measuring guidance.
Here is a fresh example, using invented dimensions and prices:
| Room | Dimensions | Gross walls | Excluded openings | Net walls |
|---|---|---|---|---|
| Study | 3 × 3.5 m; 2.4 m high | 31.2 m² | 3 m² | 28.2 m² |
| Small bedroom | 2.5 × 2.5 m; 2.2 m high | 22 m² | 2.2 m² | 19.8 m² |
| Total | 48 m² |
Assume two coats, coverage of 8 m²/L and a chosen 5% allowance. Those are example inputs, not recommended specifications. The plan requires 48 × 2 ÷ 8 × 1.05 = 12.6 L. With 2.1 L available, the shopping requirement is 10.5 L.
Five 2.5 L tins at $24 cost $120. Three 5 L tins at $43 cost $129. The smaller tin wins this single-size comparison even though the larger tin costs less per litre. After the job, the first purchase leaves 2 L; the second leaves 4.5 L, including the starting stock in both cases.
Check the decision, not just the total
The spreadsheet compares buying each size alone. If both offers are the same product, color and finish, Paint Plan can also compare a combined purchase after your explicit confirmation. In this example, two 5 L tins and one 2.5 L tin cost $110 and supply 12.5 L. That is a different shopping decision from choosing one size.
Change the assumptions before committing. Three coats would require 18.9 L before deducting stock, so the original shopping list would no longer cover the plan. An extra allowance is a planning choice; it does not replace the product’s application instructions.
A quick recovery checklist
- If the total seems too small, check metres versus centimetres and confirm the coat count.
- If a row shows an input message, finish its blue cells. Enter 0 for no openings; a blank required measurement is not zero.
- To remove a room, clear its blue cells in columns A–E, leaving the formulas intact.
- Subtract the 2.1 L stock once from the combined requirement, not once per room.
- Save a dated copy before shopping. After painting, replace estimated stock with what remains before planning the next job.
The sheet covers walls, not ceilings, trim or primer. Its costs exclude tax, delivery and supplies. Keep those items on your wider shopping list.
How this guide was prepared
Prepared by AXO Labs with AI-assisted writing and calculation checks. The worked quantities and shopping arithmetic were checked on . Dimensions, prices and allowances are invented examples, not measurements from a customer project or current shop prices.
The linked Dulux guidance supports measuring paintable area and using product-specific coverage and coats. Our example checks wall-area and whole-tin arithmetic; it does not test paint or establish that leftover paint is usable. Follow the label for your actual product. Read our editorial approach and report a correction.
Keep the plan with the project.
Use the editable sheet for your own measurements and stock. The browser tool is there when you need to explore another setup.