Square Inches Calculator
Calculate area in square inches (sq in / in²) for any shape — rectangle, circle, triangle, ellipse, trapezoid, polygon (Shoelace) and annulus. Multi-shape sum, mm/cm/ft input toggle, and instant conversion to sq ft, sq yd, sq m, cm², mm² and acres.
Quick Presets
Weight & Cost (Optional)
Enter dimensions and click Calculate to see results
Complete Guide to Square Inches
The square inch (symbol: in² or sq in) is the imperial-system unit of area equal to a square measuring one inch on each side. It sits at the small end of the area scale — useful where square feet are simply too coarse and square meters are conceptually distant. Fabric, tile, sheet metal, gaskets, dinner plates, sticker sheets, watch faces, USB ports, badges, signage cut-outs, food packaging, paper trim and circuit-board copper pours are all measured most naturally in square inches.
The relationship between square inches and larger units is fixed and exact: 1 square foot = 144 square inches, 1 square yard = 1,296 square inches, and 1 square meter ≈ 1,550 square inches (more precisely 1550.0031, derived from the exact relationship 1 in = 2.54 cm). One acre — the largest unit most people meet day-to-day — is exactly 6,272,640 square inches, which makes a vivid illustration of how much smaller a square inch is than the land-measurement units used for property deeds.
Because every common surface in a workshop, kitchen, fabric studio, signage shop or machinist’s bench has dimensions in the 1–100 inch range, square inches give you a number you can intuitively reason about. A 14-inch pizza is roughly 154 sq in; an A4 sheet of paper is about 93.5 sq in; a standard playing card is about 3.5 sq in; a 12×12 floor tile is exactly 144 sq in. Knowing these reference points helps you sanity-check any calculation in seconds.
Our Diamond Grade Square Inches Calculator handles every common shape — rectangles, circles, triangles, ellipses, trapezoids, irregular polygons via the Shoelace formula, and rings (annulus) — and lets you combine several shapes into a single total. That last feature is what separates a serious tool from a toy: real surfaces (a tiled backsplash with a window cut-out, a sheet-metal panel with mounting holes, a fabric pattern with appliques) are almost always compound, and the only honest way to get the area is shape-by-shape addition and subtraction.
Shape Reference Table
| Shape | Formula | Inputs | Typical Use |
|---|---|---|---|
| Rectangle | L × W | Length, Width | Tiles, fabric pieces, paper, signs |
| Circle | π × r² | Diameter | Plates, pizzas, lids, port openings |
| Triangle | ½ × b × h | Base, Height | Pennants, gables, bunting, panels |
| Ellipse | π × a × b | Semi-axes a, b | Oval mirrors, racetrack signage |
| Trapezoid | ½ × (a + b) × h | Parallel sides a, b, Height | Sloped roofs, gables, awnings |
| Polygon (Shoelace) | ½ | Σ (xᵢyᵢ₊₁ − xᵢ₊₁yᵢ) | | 3–8 vertex coords | Lots, custom signs, irregular cut-outs |
| Annulus (Ring) | π × (R² − r²) | Outer, inner diameter | Gaskets, washers, mats, donuts |
How to Calculate Square Inches in 5 Steps
Choose the shape from the list — rectangle, circle, triangle, ellipse, trapezoid, polygon, or annulus.
Toggle in / cm / mm / ft. The calculator converts to inches internally.
Type each measurement. The live preview updates as you type.
For compound surfaces, hit Add Shape — totals are summed automatically.
See square inches plus every common unit. Export, share, or save to history.
Use Cases & Real-World Applications
Tile, Fabric & Small Surfaces
Square inches are the natural unit for tile coverage (a 12×12 tile = exactly 144 sq in = 1 sq ft), fabric panels (a fat quarter = 18×22 in = 396 sq in), dinner plates, placemats, and craft paper. Knowing the area in square inches helps you compare to per-square-foot or per-square-meter pricing without guessing.
Need bigger surfaces? Try the Square Footage CalculatorEngineering & Machining
Gasket cross-sections, sheet-metal cut-outs, copper-pour areas on PCBs, and seal bearing surfaces are all reported in square inches in US engineering practice. The annulus mode gives ring areas for washers and gaskets directly; the polygon mode matches the area output from any DXF-aware CAD package.
Need volume? See Cubic Inches CalculatorSign Making & Print
Sign shops and print houses price by area. Polygon mode lets you drop in a logo outline directly; multi-shape sum handles cut-outs and applique. Combine with the $/sq ft input to generate instant quotes for foam-core, vinyl, dibond, and acrylic jobs.
Compare to Square Yards CalculatorInternational Conversion
Sourcing fabric from European mills, ordering tile from Italy, comparing US food packaging to EU specs — every situation that crosses imperial and metric markets needs square inches alongside cm² and m². Our calculator outputs every common unit simultaneously, so you do not have to chain converters.
Go metric: Square Meters CalculatorPro Tips
CAD vs Ruler
For production parts under 24 inches, a steel rule with 1/32" graduations is more than enough. For irregular outlines, export from CAD as DXF and read the area directly, or trace from a photograph using a known reference and feed vertex coordinates into polygon mode. CAD beats ruler whenever the part is non-orthogonal.
Irregular Shapes
Break any odd shape into the simplest sub-shapes — rectangles for the main body, half-circles for rounded ends, triangles for corners — and sum. Subtract cut-outs by adding them as separate shapes and then mentally negating, or use the polygon mode to capture the full outline at once. The Shoelace formula handles any simple polygon (no self-intersection) with full precision.
Fabric Ordering
Always add 10–15% waste to fabric calculations. Patterned fabric needs matching allowance, so push to 15–25% for stripes, plaids, or directional prints. A standard yard (36 × 44 in) is 1,584 sq in — divide your sq-in result by 1,584 to get whole yards needed, then round up.
Trusted by makers, engineers and tradespeople
“I switched from a paper-and-calculator workflow to this tool and it has cut my yardage calcs from 20 minutes to under a minute. The multi-shape sum lets me plan a whole quilt block layout, and the cm²/mm² output is gold when I source fabric from European mills.”
“Best square-inch tool I have used on the job site. The 12x12 preset and instant sq-ft conversion saves me from doing mental math in front of clients. I tap the kitchen sink preset to subtract cut-outs and the polygon mode handles awkward backsplash shapes perfectly.”
“I use this daily for gasket cross-sections and sheet-metal cut-outs. The annulus mode is a lifesaver, and the cost-per-sq-in field doubles as a quick material-budget check. Polygon (Shoelace) gives me the exact same numbers as SolidWorks to four decimal places.”
“Pricing custom signs used to take ages. Now I drop in the outline as a polygon, set my $/sq ft, and the quote is on screen instantly. Multi-shape sum handles cut-outs for logos and lettering. My estimates have never been more accurate or faster.”
Love using our calculator?
Similar Calculators
More tools in the same category
Board and Batten Layout Calculator
Calculate board and batten spacing for perfect layouts
Feet and Inches Calculator
Add, subtract, and convert feet and inches measurements
Scale Calculator
Convert between different measurement scales for plans
Square Footage Calculator
Calculate room and area square footage accurately
Lumber Weight Calculator
Calculate lumber weight from species, dimensions and quantity. 17+ wood species, kiln-dried/green/pressure-treated moisture.
Cabinet Door Size Calculator
Calculate cabinet door dimensions for full overlay, partial overlay, or inset construction. Auto hinge count.
Often Used Together
Complementary tools for complete analysis
From Other Categories
Expand your calculations
Geometry and area calculations for building
Measurement unit conversions
Project cost and budget calculations
Related Articles
Dive deeper with our expert guides and tutorials related to Square Inches Calculator