Area Calculator
Pick a shape, enter its dimensions, and get its area instantly — in your units plus square feet, square metres, and acres or hectares when the area is large enough for them to matter.
For the parallelogram, use the perpendicular height — not the slanted side length, which would overstate the area. For the circle, enter either the radius or the diameter; if both are given, the radius wins. Conversions: 1 acre = 43,560 sq ft = 4,046.86 sq m; 1 hectare = 10,000 sq m = 2.471 acres.
How it works
Rectangle: length × width. Square: side². Circle: πr² (diameter ÷ 2 gives the radius). Triangle: ½ × base × height. Trapezoid: (base a + base b) ÷ 2 × height — the average of the two parallel sides times the distance between them. Parallelogram: base × perpendicular height. Ellipse: πab, where a and b are the two semi-axes. Conversions use 1 ft = 0.3048 m exactly, so 1 sq ft = 0.092903 sq m, 1 acre = 43,560 sq ft, and 1 hectare = 10,000 sq m. Worked example: a 10 ft × 12 ft rectangle is 10 × 12 = 120 sq ft, which is 120 × 0.092903 = 11.15 sq m.
Frequently asked questions
How do I measure an irregular room or plot?
Split it into rectangles, triangles and trapezoids, calculate each piece with this calculator, and add them up. For a curved edge, approximate it with a few straight segments — the error shrinks with each extra segment.
Why does the parallelogram use height, not the slanted side?
A parallelogram is a sheared rectangle: sliding the top sideways keeps the area the same, so only the perpendicular distance between the bases matters. Using the slant side would give the area of a larger rectangle.
What is the difference between an acre and a hectare?
An acre is 43,560 square feet (about 4,047 sq m) and is the traditional US land unit; a hectare is exactly 10,000 sq m (2.471 acres) and is the metric standard. A football field without end zones is about 1.32 acres.
How accurate is the circle area?
It uses π to full double precision, so the result is exact for the radius you enter — any real-world error comes from measuring the radius, not the math. Measure the diameter across the widest point and halve it for the best radius.
When should I use the triangle calculator instead?
If you know all three sides or two sides and an angle, the Triangle Calculator gives you angles and perimeter as well as area. This page's triangle mode covers only the base-and-height case.