Combine room estimates into one material order
Group identical products before package rounding and keep different colours or specifications separate.
A project can contain several rooms without requiring a separate purchase for every room. The purchasing decision belongs to a product group. Rooms are measurements; products define the coverage, package size and other assumptions used to convert those measurements into an order.
Combine the need before rounding
Suppose one room needs 2.6 L and another needs 2.4 L after their shared product assumptions. With 2.5 L cans and no paint already owned, rounding each room separately gives two cans plus one can: 7.5 L. Combining the 5 L need first requires two cans: 5 L.
This difference comes from packaging, not from changing the measurements. Intermediate displayed values should not be fed back into the calculation. The calculator retains decimal input values and rounds only the final package count.
Keep different products separate
A shared colour name does not prove that two finishes are interchangeable. Different products, sheens, coverage assumptions, package sizes or prices need separate entries. The first version groups by the product entry you assigned, not by a text-name match.
To combine rooms, assign the same product entry to them. Creating two product entries with the same name keeps them separate. Rename entries clearly, for example “Bedroom walls — product A” and “Bathroom walls — product B”.
A box example
Two test floor areas: 8 m² and 10 m². Shared allowance: 8%. Same product covers 2.2 m² per box.
Combined plan = (8 + 10) × 1.08 = 19.44 m².
Total need = ceil(19.44 ÷ 2.2) = 9 boxes.
With two confirmed usable matching boxes owned, buy seven boxes.
Do not subtract an arbitrary area of leftover offcuts as if it were a full box. The first version accepts whole usable boxes. Whether partial packs or cut pieces can be used is a separate layout and condition question.
Take the right file
- The CSV list contains the current material's purchase quantities, specifications and assumptions in explicit SI units.
- The JSON backup contains every room and product so you can continue editing on another page or device.
- Browser printing creates a purchase summary; “save as PDF” depends on the browser's print interface.
Save the project explicitly before changing tools if you want to reuse the room list. On the next page, choose “Continue saved project”. We do not silently upload or transfer the measurements.
Try a grouped flooring order or open the paint calculator.
Sources and scope
For definitions of wallpaper match, repeat and packaging, see Brewster's product properties and Graham & Brown's wallpaper FAQ. Product instructions take precedence over generic examples. Unit conversions use the exact international foot (0.3048 m) and US liquid gallon (3.785411784 L); see NIST conversion factors.