You're on-site measuring a slab for a shed extension -- L-shape, two rooms plus a hallway. The client is waiting for a cubic metre figure for the concrete order and a square metre figure for the flooring quote. You need both before the next call.
Rectangle: L × W · Triangle: ½ × B × H · Circle: π × r²
1 What this calculator does
Calculates area (m², ft²) and volume (m³, ft³) for rectangular, triangular and circular shapes, plus room volume for ventilation and air conditioning. Supports metric and imperial. Four calculation modes selectable from the one card.
2 Formula & professional reasoning
Rectangle area = Length x Width
Triangle area = 0.5 x Base x Height
Circle area = Pi x (Diameter / 2)^2
Room volume = Length x Width x Height
All results shown in m² or m³ (and ft² or ft³ in imperial mode)
Area calculations underpin every material quantity estimate on a job -- flooring, tiling, roofing, cladding. Triangular areas arise constantly in roof work, gable ends and odd-shaped lots. Circular areas appear in slab bores, ponds and column bases. Room volume is needed for HVAC sizing, ventilation compliance and concrete volume. Getting these right from the start prevents costly under-ordering and wasted trips.
3 Worked examples
⚠️ Illustrative example only — not clinical or professional instruction.
Room 1: 6.0 x 4.5 = 27.0 m² | Room 2: 3.5 x 2.8 = 9.8 m² | Hallway: 5.0 x 1.2 = 6.0 m² | Total: 27.0+9.8+6.00.5 x 8.4 x 2.1Area: Pi x (1.8)^2 = Pi x 3.24 = 10.18 m² | Volume: 10.18 x 0.154 Sanity check
5 Common errors
| Error | Cause | Consequence | Fix |
|---|---|---|---|
| Mixing millimetres and metres in the same calculation | Reading slab depth from plans in mm and room dimensions in metres | Volume 1,000x too large or too small | Convert everything to the same unit before multiplying. If depth is 150mm, convert to 0.15m before multiplying by the area in m². |
| Calculating area without waste allowance for materials | Ordering exactly what the area calculation says | Running short on tiles, flooring or cladding -- back-order delay halts the job | For materials, add 10% waste for regular rectangular rooms. Add 15-20% for diagonal laying or complex shapes with many cuts. |
| Using the gross area for net coverage calculations | Not subtracting windows, doors and openings | Overordering paint or cladding by 5-15% on heavily windowed buildings | For wall cladding and paint: subtract the area of each window and door opening from the gross wall area before calculating materials. |
| Treating a triangle as a rectangle | Multiplying base by height without the 0.5 factor | Area doubled -- materials grossly over-ordered | Triangle area = HALF of base times height. Always multiply by 0.5. A quick check: a right-angled triangle is exactly half the rectangle that encloses it. |
6 Reference & regulatory links
7 Professional workflow
Common tools used alongside this one: