Square footage is the starting point for pricing flooring, tile, paint, sod, roofing and rent. Few rooms are perfect rectangles, so the trick is to split the space into simple shapes, find each area and add them up. This calculator covers the shapes you will meet most often and multiplies by the number of identical areas.
How to use the Square Footage Calculator
- Shape
- Length / outer length
- Width / outer width
- Side / diameter / base a
- Base b (trapezoid)
- Height
- Inner length
- Inner width
- Number of identical areas
- Waste allowance
- Price
Results update as you type, and every field accepts the units shown in its menu.
How it works
Choose the shape, enter its dimensions in feet, inches, metres or yards and the number of identical areas. The calculator returns the total area, the area to buy after the waste allowance and the cost at your price per square foot.
Typical waste allowances
| Job | Add |
|---|---|
| Carpet / sheet vinyl | 10% |
| Laminate, vinyl plank – straight | 5–10% |
| Tile – straight lay | 10% |
| Tile or plank – diagonal | 15% |
| Herringbone / chevron | 20% |
| Sod | 5% |
Tips for an accurate estimate
- Measure every dimension twice and write the unit next to each number – most estimating errors are unit mix-ups (inches entered as feet).
- Pick the unit in each field’s menu instead of converting by hand; the calculator converts everything to the same base before it multiplies.
- Round up only at the very end. Rounding each dimension first can add several percent to the final quantity.
- Suppliers sell in whole units – bags, boxes, sheets or quarter yards – so always round the final order up, not down.
Common mistakes to avoid
- Mixing square and cubic units: square feet measure area, cubic yards measure volume, and you need a depth to go from one to the other.
- Using nominal lumber sizes where actual sizes matter (a 2×4 is really 1½ × 3½ in).
- Forgetting that 1 yd³ = 27 ft³, not 9 ft³ (9 is for square yards).
Inputs explained
| Field | What to enter |
|---|---|
| Shape | Choose one: Rectangle, Square, Circle, Triangle … |
| Length / outer length | Units: ft, m, in, yd, cm |
| Width / outer width | Units: ft, m, in, yd, cm |
| Side / diameter / base a | Units: ft, m, in, yd, cm |
| Base b (trapezoid) | Units: ft, m, in, yd, cm |
| Height | Units: ft, m, in, yd, cm |
| Inner length | Units: ft, m, in, yd, cm |
| Inner width | Units: ft, m, in, yd, cm |
| Number of identical areas | A number |
| Waste allowance | In % |
| Price | Units: /ft², /m², /yd² |
What each result means
- Area to buy (with waste) = [Total area]×(1 + [Waste allowance]÷100)
- Area in square yards = [Total area]
- Material cost = [Area to buy (with waste)]×[Price]
Formula
Rectangle: A = L × W; Square: A = a²Circle: A = π × D² ÷ 4; Triangle: A = b × h ÷ 2Trapezoid: A = (a + b) ÷ 2 × h; Border: A = L × W − l × wCost = A × (1 + waste) × price per ft²Worked example
Inputs — Shape: Rectangle; Length / outer length: 12 ft; Width / outer width: 10 ft; Side / diameter / base a: 10 ft; Base b (trapezoid): 6 ft; Height: 8 ft; Inner length: 8 ft; Inner width: 6 ft; Number of identical areas: 1; Waste allowance: 10 %; Price: $4.5 /ft².
Results — Total area = 120 ft²; Area to buy (with waste) = 132 ft²; Area in square yards = 13.33 yd²; Material cost = $594.00.
Key terms
- Square foot
- Area of a square 1 ft on each side: 144 in² or 0.0929 m².
Frequently asked questions
How do I calculate square footage of an L-shaped room?
Split it into two rectangles, find each area and add them. Run the calculator once per rectangle or use the border option for a room around a central obstacle.
How do I convert square metres to square feet?
Multiply by 10.7639. One square foot is 0.0929 m².
How much waste should I add?
About 5–10% for straight-laid flooring and tile, 15% for diagonal layouts and 20% for herringbone or many cuts.
Does square footage include walls?
Real-estate floor area is usually measured to the outside of exterior walls; for materials, measure the actual surface you will cover.
What formula does the Square Footage Calculator use?
Rectangle: A = L × W; Square: A = a².