Square Footage Calculator
With length 20 ft, width 20 ft, number of identical areas 1, waste factor 10 percent and 1 more field, square footage comes to 440.0 sq ft — area to order. It is reached in 9 steps, the last of which is 400 * (1 + 10 / 100), and each one is printed on the page with its numbers filled in. The formula is the one published by ANSI Z765 residential square footage measurement standard, not an approximation fitted to it.
Square footage of a room, wall, border, gable end, ring or triangle from feet-and-inches measurements, with a waste factor and the cost.
Formula and sources checked · How we check
Shape Rectangle, Length 20 ft, Width 20 ft, Number of identical areas 1
440.0 sq ft
Area to order for the inputs in this link. Editing a field recomputes the calculator below; this figure holds the answer the page was loaded with.
It is written into the HTML rather than drawn by a script, so a search engine reading this page without running JavaScript still finds an answer.
- The three sides close into a triangle
1- Area of the openings
2 * 3 * 530 sq ft- Area per shape
400 sq ft- Total area
400 * 1400 sq ft- Area to order
400 * (1 + 10 / 100)440 sq ft- Same area in square meters
440 * 0.09290340.877 sq m- Same area in square yards
440 / 948.889 sq yd- Same area in acres
440 / 435600.01 acres- Material at that price
440 * 0$0
Several at once
A job is rarely one of anything. Work out the first, add it, change the figures and add the next — the list keeps what each line was, and totals them.
Worked example
A 12'6" × 10'3" room is 128.1 sq ft. Order 141 sq ft to cover a 10% waste factor — flooring is sold by the carton, so round up to the next full carton after that.
How to work it out yourself
- 1.Measure wall to wall in feet and inches, with the baseboards off — flooring runs underneath them.
- 2.Pick the shape that matches what you are measuring. A wall with a door and windows subtracts them; a border counts only the path and not the patio inside it; a gable end is a trapezoid with the shorter side set to zero.
- 3.If you can reach all three sides of a triangle but not its height, measure the sides and use the second triangle mode. It is the same area by a different route.
- 4.Split an L-shaped room into rectangles and add the parts. Multiplying the longest length by the widest width overstates it by the missing corner.
- 5.Add the waste factor for your layout: 10% straight-lay, 15% diagonal, 20% herringbone.
- 6.Round up to whole cartons, and buy them from one dye lot so a later repair still matches.
How far one cubic yard goes
A cubic yard is 27 cubic feet. Spread one inch deep it covers 324 square feet, and every other depth is that figure divided by the depth in inches — which is the whole table in one sentence.
| Depth | Square feet | Square yards |
|---|---|---|
| 1 in | 324 | 36.0 |
| 2 in | 162 | 18.0 |
| 3 in | 108 | 12.0 |
| 4 in | 81 | 9.0 |
| 6 in | 54 | 6.0 |
| 8 in | 41 | 4.5 |
| 10 in | 32 | 3.6 |
| 12 in | 27 | 3.0 |
Cubic yards for a given area
| Area | 1 in | 2 in | 3 in | 4 in | 6 in | 8 in | 10 in | 12 in |
|---|---|---|---|---|---|---|---|---|
| 100 sq ft | 0.31 | 0.62 | 0.93 | 1.23 | 1.85 | 2.47 | 3.09 | 3.70 |
| 200 sq ft | 0.62 | 1.23 | 1.85 | 2.47 | 3.70 | 4.94 | 6.17 | 7.41 |
| 500 sq ft | 1.54 | 3.09 | 4.63 | 6.17 | 9.26 | 12.35 | 15.43 | 18.52 |
| 1,000 sq ft | 3.09 | 6.17 | 9.26 | 12.35 | 18.52 | 24.69 | 30.86 | 37.04 |
Suppliers deliver in whole or half yards, so round up — a truck will not bring 2.37.
Bags to the cubic yard
| Bag | Holds | Bags per yard |
|---|---|---|
| Mulch, 2 cu ft bag | 2 cu ft | 14 |
| Mulch, 3 cu ft bag | 3 cu ft | 9 |
| Topsoil or compost, 1 cu ft bag | 1 cu ft | 27 |
| Concrete mix, 80 lb bag | 0.6 cu ft | 45 |
| Concrete mix, 60 lb bag | 0.45 cu ft | 60 |
| Concrete mix, 40 lb bag | 0.3 cu ft | 90 |
Concrete is sold by weight and the yield is printed on the bag, which is why it takes 45 of the 80 lb bags to make a yard rather than the dozen people expect. Past about ten bags, ready-mix is cheaper and far less work.
Depth by use
| Use | Depth | Why |
|---|---|---|
| Mulch, established beds | 2–3 in | Deeper than 3 in holds water against stems and starves roots of air. |
| Mulch, new beds over bare soil | 3–4 in | The extra inch is what suppresses weeds for a season. |
| Topsoil over an existing lawn | 0.25–0.5 in | Any more and the grass underneath is smothered rather than fed. |
| Topsoil for a new lawn | 4–6 in | Roots need the depth once, at the start; it cannot be added later. |
| Gravel walkway | 2–4 in | Over a compacted base, not over soil. |
| Gravel driveway, surface course | 3–4 in | Over 6 to 8 in of compacted base. |
| Gravel driveway, full build | 8–12 in | Base and surface together, laid and compacted in layers. |
| Concrete patio or walkway | 4 in | Four inches is the ordinary residential slab. Follow the specification for anything carrying a vehicle. |
How much extra to order
| Reason | Add | Note |
|---|---|---|
| Compaction, crushed stone | 20% | Six inches loose settles to about five. Order for the finished depth. |
| Settling, mulch and soil | 10–15% | Organic material shrinks as it breaks down over the first season. |
| Spillage and uneven ground | 5–10% | A hole is never the rectangle it was measured as. |
| Concrete, sub-base variation | 5–10% | A slab poured half an inch deep over 200 sq ft is a third of a yard nobody ordered. |
The formula
- The three sides close into a triangle
- Area of the openings
2 * 3 * 5 - Area per shape
- Total area
400 * 1 - Area to order
400 * (1 + 10 / 100) - Same area in square meters
440 * 0.092903 - Same area in square yards
440 / 9 - Same area in acres
440 / 43560 - Material at that price
440 * 0
Source: ANSI Z765 residential square footage measurement standard, NIST Office of Weights and Measures
Questions people actually ask
- How much waste should I add?
- Straight-lay plank or tile: 10%. Diagonal layouts: 15%. Herringbone or chevron: 20%. Waste is cut-off, not spare — the offcut from one row rarely starts the next unless the room is a clean multiple of the plank length.
- Do I measure to the wall or to the baseboard?
- Measure wall to wall with baseboards removed, since flooring runs under them. Measuring to the face of an installed baseboard undercounts by roughly 0.5–1 in per wall.
- How do I handle an L-shaped room?
- Split it into rectangles, run each through the calculator, and add the results. Do not multiply the longest length by the widest width; that overstates an L-shape by the area of the missing corner.
- How do I measure a wall with a door and two windows?
- Use the wall shape: enter the wall, then the number of openings and the size of one. It subtracts them. For paint most decorators do not deduct anything under about 20 sq ft, because the cutting-in around an opening uses roughly what the opening saves; for drywall and panelling you deduct every one.
- What shape is a gable end?
- A triangle, which is a trapezoid with its shorter parallel side set to zero. Use the trapezoid mode and enter zero for the shorter side, or the triangle mode with the base and the peak height. A hipped or clipped gable is a genuine trapezoid, which is why the mode takes both parallel sides.
- What counts as square footage when selling a house?
- ANSI Z765 counts finished, heated space measured to the exterior wall face, and excludes garages and most below-grade rooms. That is why an appraisal often lands well under the number a listing quotes.
Related
- Concrete CalculatorCubic yards of concrete for a slab, round pad, footing, column, wall or stairs, with bag counts and cost.
- Tile CalculatorHow many tiles and boxes to order for a floor or wall, with the waste factor the layout actually needs.
- Circle CalculatorArea, circumference and radius of a circle from its diameter — in square feet and square inches.
- Board Foot CalculatorConvert lumber dimensions to board feet and price out a cut list, including nominal-vs-actual sizing.
- Paint CalculatorGallons of paint for a room, after subtracting doors and windows and allowing for the number of coats.
- Deck Board CalculatorDecking boards, joists and fasteners for a rectangular deck, accounting for the gap between boards.
Part of a job
- Building a deck — 7 pages, in the order the questions arrive
- Pouring concrete — 6 pages, in the order the questions arrive
- Painting a room — 5 pages, in the order the questions arrive
Worked out already
The same calculator with the numbers filled in. Each one computes on the server, so the answer is in the page rather than waiting on a click.
Read first
- How to Read a Tape Measure — Why the marks are different lengths, and how to read a sixteenth without counting them: each halving is drawn one step shorter than the one above it.
- How to Measure a Room for Flooring — Where to hold the tape, how to split an odd shape into rectangles rather than one clever polygon, and how much extra to order once the offcuts are counted.
- What a Concrete Patio Costs — Materials, delivery and labour for a slab, and where the price actually moves: on a small pour the concrete is rarely the largest of the three figures.
- What a Deck Costs to Build — Decking, framing and fasteners priced out, and why the board decides the total: the framing under it barely changes between a cheap deck and a costly one.
- What a Shingle Roof Costs — Squares, bundles, tear-off and the pitch multiplier that makes a steep roof cost more twice over — once for the area, once for the labour of standing on it.
- What a Fence Costs — Post spacing, the ground-contact rating most people buy wrong, and why corners and gates cost more per foot than the long straight runs between them.
- What Drywalling a Room Costs — Sheets, screws, and the finish level that decides most of the labour bill while appearing on no quote — level 4 and level 5 are not the same job.
- What a Gravel Driveway Costs — Which stone actually compacts, how deep each layer goes, and why the cheapest load is the expensive one once it has to be dug out and replaced two years later.
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<iframe src="https://rulecalculators.com/embed/square-footage" width="100%" height="420" style="border:1px solid #e7e4de;border-radius:12px" title="Square Footage Calculator"></iframe>Straight to your case
The control above covers every case. These are the same calculator fixed to one of them, with the formula for that case written out.
- Square Footage of a CircleFrom Diameter
- Square Footage of a TriangleGable Ends