📐 Square Footage Calculator
Add up the square footage of rooms and odd shapes — rectangles, circles, triangles, trapezoids — subtract cut-outs, and estimate cost per square foot.
What Square Footage Calculator Does
This square footage calculator adds up any number of areas — rooms, hallways, a patio, an irregular yard — each as a rectangle, circle, triangle or trapezoid, and lets you subtract cut-outs such as a kitchen island or a stair opening. Measure in feet, inches, yards, meters or centimeters; the total is always shown in square feet, square yards, square meters and acres, with an optional cost at your price per square foot.
Most rooms that are not rectangles are made of rectangles. An L-shaped living room is two rectangles; a bay window is a rectangle plus a trapezoid. Break the space into simple shapes, measure each, and add them here — the same way flooring installers and estimators do it.
How to Use Square Footage Calculator
- Pick the unit you measured in (feet, inches, yards, meters or centimeters)
- Enter each room or section, choosing its shape
- Add more areas, or subtract cut-outs like islands and stair openings
- Read the total in square feet, square yards, square meters and acres
- Enter a price per square foot for a cost estimate
Formula Used by Square Footage Calculator
Area formulas used
Rectangle = L × W · Circle = π × r² · Triangle = ½ × b × h · Trapezoid = ½ × (a + b) × h
Worked example
A 14 × 16 ft living room and a 12 × 12 ft bedroom.
- 14 × 16 = 224 sq ft
- 12 × 12 = 144 sq ft
- 224 + 144
Result: 368 sq ft (40.9 sq yd, 34.2 m²).
Converting measurements
1 sq yd = 9 sq ft · 1 m² ≈ 10.764 sq ft · 1 acre = 43,560 sq ft · 1 sq ft = 144 sq in
Area Conversions
| From | To square feet |
|---|---|
| 1 square inch | 0.00694 sq ft (1/144) |
| 1 square yard | 9 sq ft |
| 1 square meter | 10.764 sq ft |
| 1 acre | 43,560 sq ft |
| A 10 ft diameter circle | 78.54 sq ft |
What Counts in a Home’s Official Square Footage (ANSI Z765-2021)
The measurement standard Fannie Mae requires appraisers to use for single-family homes since April 1, 2022.
| Counts as living area | Does not count |
|---|---|
| Finished, heated space above grade | Garages |
| Measured to the exterior walls | Unfinished areas |
| Ceiling height of at least 7 ft (with limited exceptions) | Below-grade basements, even if finished (reported separately) |
| Finished stairs, counted on the level they descend from | Open-to-below areas such as two-story foyers |
Source: Fannie Mae — Standardizing Property Measuring Guidelines
How to Read Your Result
Why your total differs from the listing
Listings based on ANSI Z765 measure to the outside of exterior walls, so wall thickness is included, and they exclude basements and garages. A sum of interior room measurements is therefore usually smaller than the listed figure — by several percent for a typical house.
Buying materials
Flooring, tile and sod are sold with waste allowances: add about 5–10% for straight layouts and more for diagonal patterns or rooms with many corners. Paint coverage is based on wall area, not floor area.
Limitations & Accuracy Notes
- Irregular curves must be approximated with the available shapes; the result is only as accurate as the measurements entered.
- Totals are floor areas — wall or roof area needs its own calculation.
- For appraisals or listings, only a measurement made to the ANSI Z765 standard (or your state’s rules) counts as official.
Frequently Asked Questions
How do I calculate square footage?
How do I measure a room with inches?
How do I calculate the square footage of a circle or triangle?
How do I subtract an area, like a kitchen island?
How is a home’s official square footage measured?
How many square feet are in a square yard or an acre?
How much extra flooring should I buy?
References & Further Reading
- Fannie Mae — Standardizing Property Measuring Guidelines (ANSI Z765-2021) — Requirement effective April 1, 2022