Wall Area Calculator
Wall area (sq ft)
96.0
How it works
Accurate wall area calculation is the foundation of any painting, wallpaper, panelling, or tiling project. Under-estimating means running short mid-project; over-estimating wastes material budget. The Wall Area Calculator handles rectangular rooms, L-shaped rooms, rooms with sloped ceilings, and lets you subtract door, window, and other opening areas.
**Basic rectangular room** Perimeter = 2 × (length + width). Wall area = perimeter × ceiling_height. For a standard room 4m × 5m with 2.4m ceilings: perimeter = 18m; wall area = 43.2 m². Add ceiling: 4 × 5 = 20 m². Subtract doors (standard = ~1.6 m² each) and windows (~1.1 m² each).
**Sloped ceilings (triangular wall sections)** For rooms with vaulted or sloped ceilings, the triangular section above the knee wall adds area. Triangular area = (base × height) / 2. In a gable-end wall with base 4m and gable height 2m above the main wall: triangular area = (4 × 2) / 2 = 4 m² extra.
**L-shaped rooms** Decompose into two rectangles. Calculate each rectangle's perimeter, but subtract the shared interior corners (wall sections where rooms meet). The calculator guides you through this decomposition.
**Material quantity from area** Paint: divide total area by coverage rate (typically 10 m²/litre). Wallpaper: divide area by roll coverage (standard UK roll = 5.3 m², US roll ≈ 5.0 m² usable). Tiles: divide area by tile size, add 10–15% for cuts and waste. The calculator outputs quantities for all three materials simultaneously.
Privacy: all calculations run in the browser. No data is transmitted.
Frequently Asked Questions
- Measure from doorframe to doorframe or from corner to corner (you don't need to move furniture against walls). For width and length, measure at the floor level — measure both dimensions at least twice (rooms are rarely perfectly rectangular). Measure ceiling height from floor to ceiling at one corner. For sloped ceilings, measure both the low-eave height and the ridge height plus the width at that point to calculate the triangular section. You can measure over furniture for height — use a tape measure extended vertically or a laser distance measurer (accurate to ±2mm, works well for rooms up to 20m).
- A 12×12 ft room (same dimensions as above): ~325 sq ft net wall area. Standard US double roll: ~56 sq ft per roll (double roll standard = 27 inches wide × 25 yards = 56 sq ft usable, allowing for pattern matching waste). 325 / 56 ≈ 5.8 → buy 6 double rolls. For patterned wallpaper with a 24-inch pattern repeat: add 15–25% extra for matching patterns at seams — buy 7–8 double rolls. UK standard roll: 10m × 520mm = ~5.2 m² per roll. 30.2 m² / 5.2 = 5.8 → 6 rolls minimum; buy 7 for safety.
- It depends on your project. This calculator separates wall area and ceiling area: wall area = perimeter × height − openings; ceiling area = length × width. If you're calculating paint for walls only (keeping the existing ceiling colour), use wall area only. If painting both, add ceiling area. Many painters use a different paint finish for ceilings (flat/matte ceiling white) than walls (eggshell or satin) — calculating them separately lets you buy the right type and amount of each product.
- Heavy orange-peel or knockdown texture increases paint consumption by 15–25% because the textured surface has more total area than a flat surface (the peaks and valleys add surface area). It also holds more paint per coat. New textured drywall absorbs significantly more primer and first coat than smooth drywall. For tile quantities, textured walls don't affect tile area — tiles cover the wall area regardless of texture. For wallpaper, surface texture makes installation harder and you need to sand or skim-coat the texture before hanging wallpaper.