Square Feet to Square Inches Calculator
Convert square feet to square inches: 1 sq ft = 144 sq in, exactly, because a square foot is 12 in × 12 in. Type either box — it runs both ways.
Last updated:Conversion Formula
Conversion factors follow NIST Special Publication 811, Appendix B.9.1 (area). Links are in Sources below.
square inches = square feet × 144
square feet = square inches ÷ 144 (1 sq in = 1/144 sq ft = 0.006944444444444444 sq ft — the 4 repeats)
144 is definitional, not measured, so neither direction carries rounding error. The same holds in metric: NIST prints 1 sq in = 6.4516 E−04 m² and 1 sq ft = 9.290 304 E−02 m², and 0.09290304 ÷ 0.00064516 = 144 exactly.
Worked Example
A shelf board is 2 ft deep × 3 ft long. You want to cover the top with a veneer sheet sold by the square inch. How much do you need?
- Area in sq ft: 2 × 3 = 6 sq ft.
- Convert: 6 × 144 = 864 sq in.
- Cross-check in inches first: 24 in × 36 in = 864 sq in. ✓ Same answer, which is the point — convert the sides or convert the area, but not both.
Now the mistake that costs money: a 12 in × 12 in offcut is 144 sq in = 1 sq ft, but a 12 in × 6 in offcut is 72 sq in = 0.5 sq ft. Halving one side halves the area; halving both sides quarters it.
Quick Reference
| Square Feet | Square Inches |
|---|---|
| 1/144 sq ft | 1 sq in |
| 1/12 sq ft | 12 sq in |
| 1/9 sq ft | 16 sq in |
| 1/4 sq ft | 36 sq in |
| 1/2 sq ft | 72 sq in |
| 1 sq ft | 144 sq in |
| 2 sq ft | 288 sq in |
| 3 sq ft | 432 sq in |
| 5 sq ft | 720 sq in |
| 9 sq ft (1 sq yd) | 1,296 sq in |
| 10 sq ft | 1,440 sq in |
| 25 sq ft | 3,600 sq in |
| 50 sq ft | 7,200 sq in |
| 100 sq ft | 14,400 sq in |
| 4,840 sq ft (1/9 acre) | 696,960 sq in |
| 43,560 sq ft (1 acre) | 6,272,640 sq in |
| 27,878,400 sq ft (1 sq mi) | 4,014,489,600 sq in |
What is a square inch?
A square inch is the area of a square one inch on each side. The inch itself is exact by international agreement: since the 1959 definition, 1 ft = 0.3048 m exactly, and because 1 ft = 12 in, 1 in = 0.0254 m exactly. Squaring that gives 0.0254² = 0.00064516 m² = 6.4516 cm², which is the figure NIST SP 811 prints as 6.4516 E−04 m².
Because 2.54 cm is exact, the square inch is one of the few imperial area units with a terminating metric value. There is no survey-inch variant to worry about: the survey/international split affects the foot at the 2 ppm level, and its whole effect on an acre is, in the words of the Federal Register notice retiring the survey foot, "about 0.17 ft² or 25 square inches."
What is a square foot?
A square foot is the area of a square one foot on each side: 12 in × 12 in = 144 sq in, or 0.09290304 m² exactly (NIST prints 9.290 304 E−02 m²). It is the unit US building trades, real-estate listings, and flooring orders use, which is why a small-shop measurement in inches has to be scaled up before it can be compared against a sq ft price.
One square foot also equals 1/9 sq yd, 1/43,560 acre, and 0.09290304 m². The sq ft to sq yd page covers the yard step.
What rectangles make exactly 144 square inches?
144 has eight whole-number factor pairs, which is why a square foot shows up in so many tidy shapes. Useful when you are checking a cutting list against an offcut:
| Shape | Dimensions (inches) | Check |
|---|---|---|
| Square (the definition) | 12 × 12 | √144 = 12 |
| Near-square | 9 × 16 | 9 × 16 = 144 |
| Wide rectangle | 8 × 18 | 8 × 18 = 144 |
| Board offcut | 6 × 24 | 6 in wide × 2 ft long |
| Narrow strip | 4 × 36 | 4 in wide × 3 ft long |
| Trim strip | 3 × 48 | 3 in wide × 4 ft long |
| Band | 2 × 72 | 2 in wide × 6 ft long |
| Lineal foot of 1-in band | 1 × 144 | 1 in wide × 12 ft long |
| Circle of the same area | diameter 13.54 in | √(144 × 4 ÷ π) = 13.5406 |
Perimeter varies wildly even though the area does not: the 12 × 12 square needs 48 in of edge banding, the 1 × 144 strip needs 290 in. If you are pricing trim or tape, convert the shape, not just the area — the property size calculator does the same job for lots.
Linear inches are not square inches
This is the single most common error on this conversion, and it is not a rounding error — it is a dimensional one.
- You cannot convert sq ft to a length. 6 sq ft tells you nothing about how long the piece is. Six square feet could be 2 ft × 3 ft, 1 ft × 6 ft, or 2.449 ft × 2.449 ft.
- Multiply the sides in inches, not the area twice. A board 96 in × 5.5 in is 96 × 5.5 = 528 sq in. Divide by 144 once: 3.6667 sq ft. Converting each side to feet first (8 ft × 0.4583 ft) gives the same 3.6667 sq ft.
- Fractional inches round the wrong way for cutting. 5.5 in is exact; 5 ⅝ in is 5.625; but 5.4 in is not 5 ⅜ in (5.375). Keep the decimal until the last step, then round up for a cut and down for a fit.
- Kerf and waste are lengths, not areas. A 1/8 in saw blade removes 1/8 in of length per cut, which on a 5.5 in wide board is 0.6875 sq in per cross-cut. Add it per cut, not as a percentage.
FAQ
Why is 1 square foot equal to 144 square inches and not 12?
A square foot has two sides of 12 inches each, and area multiplies the two: 12 in × 12 in = 144 sq in. Twelve square inches is a 1 in × 12 in strip, which is one-twelfth of a square foot. Any linear-to-area conversion squares the factor, which is why 1 sq yd = 9 sq ft and not 3, and 1 sq mi = 27,878,400 sq ft and not 5,280.
Is the 144 factor exact or rounded?
Exact, and provable two ways. By definition 1 ft = 12 in, so 12 × 12 = 144 with no measurement involved. In metric, NIST SP 811 gives 1 sq in = 6.4516 E−04 m² and 1 sq ft = 9.290 304 E−02 m², and 0.09290304 ÷ 0.00064516 = 144 exactly. Because it is exact there is no rounding error to carry, unlike conversions through metres.
How do I convert square inches back to square feet?
Divide by 144, or multiply by 1/144 = 0.006944444444444444 (the 4 repeats forever). Example: 864 sq in ÷ 144 = 6 sq ft. The converter above runs this direction if you type into the second box, or use the square inches to square feet page.
How many square inches are in a square yard, an acre, or a square mile?
1 sq yd = 1,296 sq in (9 × 144). 1 acre = 6,272,640 sq in (43,560 × 144). 1 sq mi = 4,014,489,600 sq in (27,878,400 × 144). 1 hectare = 15,500,031.000062 sq in, which is not a whole number because the hectare is defined in metres.
What is the difference between linear inches and square inches?
Linear inches measure one edge; square inches measure a surface, and they do not convert by a single number without knowing both dimensions. A board 96 in long and 5.5 in wide is 528 sq in, or 3.67 sq ft. Ordering by the wrong one is the most common way a cutting list ends up short.
When should I use square inches instead of square feet?
When the piece is smaller than about a square foot and the decimal gets in the way: quilting and sewing pattern pieces, decals and vinyl lettering, gasket and shim stock, screen and filter media, package label area, and full-size engineering drawings. Above a few square feet the numbers get long fast, which is why building trades stay in sq ft.
Sources and How to Check This Page
- Area factors — square inch 6.4516 E−04 m², square foot 9.290 304 E−02 m², square yard 8.361 274 E−01 m², square mile 2.589 988 E+06 m² — are transcribed from NIST Special Publication 811, Appendix B.9.1.
- The exactness of the inch and foot comes from the 1959 international definition, quoted in 85 FR 62698, FR Doc. 2020-21902: "one foot being equal to 0.3048 meter (exactly)", named the international foot in the 1959 notice at 24 FR 5348. The same document states that the survey-foot/international-foot difference in area for 1 acre is "about 0.17 ft² or 25 square inches".
- 12 × 12 = 144, 9 × 144 = 1,296, 43,560 × 144 = 6,272,640, 27,878,400 × 144 = 4,014,489,600, 0.0254² = 0.00064516, 0.09290304 ÷ 0.00064516 = 144, √144 = 12, √(144 × 4 ÷ π) = 13.5406, 8 × 18 = 9 × 16 = 6 × 24 = 144. Every other number here is arithmetic on those, so the whole page can be re-derived with a calculator.
- What this page does not claim: bulk densities, material prices, or how much waste to add for a specific product. Those vary by supplier and are sourced on the pages that use them — see sq ft to cubic feet for material volumes.