Compute area in cm² from rectangle, circle, triangle, trapezoid, parallelogram, and regular polygon dimensions.
Convert to other area units
Common cm² references (tap to load as rectangle)
These fill the Rectangle tab with real-world sheet dimensions.
Area formulas
Rectangle and square
Multiply the two perpendicular side lengths. For a square, both sides are equal, so the area is the side squared.
Circle
Uses the radius (half of the diameter). Pi (π) is approximately 3.14159.
Triangle
Two common methods. Base-and-height uses a side and the perpendicular drop to the opposite vertex. Heron's formula needs only the three side lengths.
Trapezoid
Average the two parallel bases and multiply by the perpendicular distance between them.
Parallelogram
Base times perpendicular height. The slanted side length is not used — only the vertical height matters.
Regular polygon
A polygon with n equal sides of length s. The cotangent of π/n captures how much area each triangular slice contributes.
Unit conversions
Square units scale by the square of the linear ratio. For example, 1 cm = 10 mm, so 1 cm² = 100 mm².
Quick reference — common sheet areas
| Object | Dimensions | Area (cm²) |
|---|---|---|
| Credit card (ISO 7810 ID-1) | 85.6 × 54 mm | 46.22 |
| US business card | 88.9 × 50.8 mm | 45.16 |
| Post-it note (standard) | 76 × 76 mm | 57.76 |
| Passport photo | 35 × 45 mm | 15.75 |
| Paper A6 | 105 × 148 mm | 155.40 |
| Paper A5 | 148 × 210 mm | 310.80 |
| Paper A4 | 210 × 297 mm | 623.70 |
| Paper A3 | 297 × 420 mm | 1,247.40 |
| US Letter | 8.5 × 11 in | 603.23 |
FAQ
What is a square centimeter (cm²)?
A square centimeter is the area of a square whose sides are exactly 1 cm long. It is the standard metric unit for measuring small areas — postcards, fabric scraps, wounds, skin patches, microscope fields. One cm² equals 100 mm² (a grid of ten-by-ten millimeter squares) and 0.0001 m² (one ten-thousandth of a square meter).
How do I convert cm² to m²?
Divide by 10,000. The linear ratio is 1 m = 100 cm, so the area ratio is 100 × 100 = 10,000. For example, 500 cm² ÷ 10,000 = 0.05 m², and 2,500 cm² = 0.25 m². Going the other way, multiply m² by 10,000 to get cm².
What is the difference between cm and cm²?
A centimeter (cm) measures length in one dimension — a single line or edge. A square centimeter (cm²) measures area in two dimensions — the space inside a shape. You cannot convert directly between them because they measure different quantities. A 10 cm line has no area; a 10 cm × 10 cm square has an area of 100 cm².
How do I find the area of an irregular shape?
Split it into simpler shapes whose areas you can compute — rectangles, triangles, trapezoids — then add the parts. For curved outlines, count grid squares on graph paper or use the trapezoidal rule. For shapes defined by vertex coordinates, the shoelace formula gives an exact answer without decomposition.
What is cm² used for in real life?
Dentistry and dermatology track wound area, lesion size, and tooth surface in cm². Crafts, sewing, and scrapbooking use it to estimate fabric, paper, or vinyl waste. Printing quotes small-format jobs by cm². Physics and electronics use it for cross-sections. In daily life, it helps size labels, stickers, patches, and screen protectors.
Compute area in square centimeters for six shapes: rectangle, circle, triangle (base-height or three sides via Heron), trapezoid, parallelogram, and regular polygon from 3 to 12 sides. Each input accepts millimeters, centimeters, meters, or inches and auto-converts to cm² for the result. Every answer also appears in mm², m², in², ft², and yd² with copy buttons. Example 1: a standard credit card at 85.6 × 54 mm gives 46.22 cm² (0.004622 m²). Example 2: an A4 paper sheet at 210 × 297 mm gives 623.70 cm² (≈ 96.65 in²). An optional price-per-cm² mode divides total cost by area, useful for fabric, vinyl, and printing quotes. Preset buttons load common sheet sizes (credit card, business card, post-it, A3/A4/A5/A6, US Letter, passport photo) straight into the rectangle panel.