Area Calculator
Choose a shape, enter dimensions, and see the step-by-step area calculation with a clean final result.
Your shape
Preview
Final area
Results interpretation
- Units matter: switching cm → m changes the numeric result by a factor of 10,000 because area is squared.
- Pick the right formula: triangles accept base-height or three sides (Heron). Use the inputs you actually know.
- Check plausibility: zero or negative values aren’t valid dimensions; this tool ignores them.
- Rounding: your decimal places setting only affects display, not the internal math.
How this calculator works
Each shape uses its standard area formula. Inputs are converted to meters internally so we can stay unit-safe; the final answer is converted back to your chosen unit squared.
Show formulas
- Rectangle:
A = w·h - Square:
A = s² - Circle:
A = πr² - Triangle (base/height):
A = ½bh - Triangle (Heron):
A = √[s(s−a)(s−b)(s−c)],s=(a+b+c)/2 - Trapezoid:
A = ½(b₁+b₂)h - Ellipse:
A = πab(semi-axes) - Parallelogram:
A = bh - Sector:
A = (θ/360)πr² - Regular polygon:
A = n s² / (4 tan(π/n))
FAQ
What units does the calculator support?
Centimeters, meters, inches, and feet. Results display as squared units (cm², m², in², ft²).
Do I need all triangle sides?
No. Use base + height if that’s easier. Otherwise enter all three sides and we’ll apply Heron’s formula.
Why did my number change so much when I switched units?
Area scales with the square of the conversion factor. For example, 1 m = 100 cm, so 1 m² = 10,000 cm².
Can I calculate irregular shapes?
Approximate by splitting the shape into rectangles/triangles and summing their areas.
What about perimeter?
This tool focuses on area. Try the Triangle or Circle tools for more geometry features.
Use cases & examples
- Flooring: A 12 ft × 10 ft room → 120 ft² of coverage.
- Round table: Radius 20 in → 1257 in² of surface area.
- Garden bed (trapezoid): Bases 3 m and 4 m, height 2 m → 7 m².
What this Area Calculator does
Area calculator results help you size materials, compare designs, and check homework quickly. This page supports rectangle, square, circle, triangle (base-height or Heron), trapezoid, ellipse, parallelogram, sector, and regular polygon, with instant feedback as you type.
How to use this tool
Pick your shape, choose units, and enter the dimensions you know. The amber banner shows the steps and the exact formula; the green banner shows the final area in your chosen units. You can change decimal places to control rounding.
Why units matter
Area is two-dimensional. Doubling a length multiplies area by four; converting length units multiplies area by the square of the conversion factor. Keep inputs consistent and use the unit selector for the output.
Common pitfalls
- Using diameter where the formula expects radius (circle).
- Mixing units (inches with centimeters) in one calculation.
- Triangle “height” must be perpendicular to the base.
Limitations
We assume ideal, flat shapes without cutouts. For irregular regions, split into simpler shapes and sum areas.