NumberTally Area Calculator
Find the area of a rectangle, triangle, circle, or trapezoid in seconds. Pick the shape, enter the measurements, and get the area with the formula and step-by-step working — plus the answer in square meters, square feet, and acres. Free, no sign-up.
Advanced options
The four area formulas
Rectangle: length × width. Triangle: half the enclosing rectangle, ½ × base × height. Circle: πr² — imagine unrolling the circle into a near-parallelogram. Trapezoid: the average of the two bases times the height, ½(a+b)h.
Why square units
Area counts how many unit squares fit inside a shape, so it's always in square units: cm², m², ft². The converter below translates your answer into square meters, square feet, and acres (1 acre = 4,046.86 m²) for land-sized areas.
Frequently Asked Questions
How do you find the area of a circle?
A = πr² — pi times the radius squared. A circle of radius 5 has area 25π ≈ 78.54.
How do you find the area of a triangle?
A = ½ × base × height, where the height is measured perpendicular to the base. Any triangle is exactly half of a rectangle with the same base and height.
How do you find the area of a trapezoid?
A = ½(a + b) × h — average the two parallel bases, then multiply by the height between them.
Why is area measured in square units?
Because area counts unit squares: a 4×5 rectangle holds exactly twenty 1×1 squares, hence 20 square units.
What if I measured the diameter, not the radius?
Tick the diameter checkbox and the calculator halves it for you — or use A = πd²/4 directly.