Measure an L-shaped floor without double-counting
Use two non-overlapping rectangles and check against an outer-rectangle subtraction example.
An L-shaped floor is a useful case for checking what a room-area tool actually does. The rectangular model is still useful when you divide the shape carefully. The goal is to count every part once.
Make two rectangles that do not overlap
Draw the outline and mark the inside corner. Extend one line from that corner to the outer edge. The two resulting rectangles should share an edge but no floor area. Record both sets of dimensions and assign the same flooring product to both entries.
In this tool, the two entries may be named “L-room — main section” and “L-room — return”. Their areas combine before the same product's allowance and whole-box rounding. Do not use these two floor pieces as a wall-paint model: the split introduces an internal edge that is not a real wall.
Check the area two ways
Test outline: outer rectangle 5 m × 4 m, with a missing corner 2 m × 1 m.
Outer-minus-missing method: 20 − 2 = 18 m².
Non-overlapping rectangles: 5 × 3 = 15 m² and 3 × 1 = 3 m².
Combined area: 18 m². With entered 8% allowance and 2.2 m² per box, buy nine boxes when none are already owned.
The two methods agree. If your sketch produces different answers, inspect which section is missing, which measurements include the full span, and whether the rectangles overlap.
The common double-counting mistake
Adding 5 × 3 and 3 × 4 would give 27 m² because those rectangles overlap over a 3 × 3 m area. That result exceeds the entire 20 m² outer rectangle, which is a useful sign that something is wrong.
The calculator cannot infer the shape from two entered rectangles, so it cannot automatically detect this geometric overlap. The measurement sketch and area cross-check remain part of the user's process.
What this estimate does not establish
Area alone does not specify which way the material runs, where joints land or how offcuts are reused. Stairs, sloping surfaces and complex patterns need separate measurement and installation decisions. Use actual product coverage and an allowance appropriate to your project.
Enter the two floor sections, and use the box and allowance guide to understand the purchase result.
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.