Area Formulas Cheat Sheet: Rectangles, Circles, Triangles & More
September 18, 2026
Every shape's area formula follows the same basic idea — multiply two dimensions that together describe the enclosed space — but the exact formula varies by shape. Here's a complete reference table.
Skip the math and get your answer instantly:
Open the Area Calculator →Area Formula Reference Table
| Shape | Formula |
|---|---|
| Square | s² |
| Rectangle | l × w |
| Triangle | ½ × b × h |
| Circle | π × r² |
| Trapezoid | ½ × (b1 + b2) × h |
| Parallelogram | b × h |
| Ellipse | π × a × b (semi-axes) |
| Regular polygon | ½ × perimeter × apothem |
Worked Example: Trapezoid
A trapezoid with parallel sides of 8 and 12 units and a height of 5 units: Area = ½ × (8 + 12) × 5 = ½ × 20 × 5 = 50 square units.
Combining Shapes for Irregular Areas
Most real-world spaces — an L-shaped room, an irregular lot — aren't a single textbook shape. Break the space into rectangles, triangles, and trapezoids you can calculate individually, then add all the areas together for the total.
Frequently Asked Questions
What's the area formula for a trapezoid?
Area = ½ × (base1 + base2) × height, where base1 and base2 are the two parallel sides.
How do I find the area of an ellipse?
Area = π × a × b, where a and b are the lengths of the semi-major and semi-minor axes (half the full width and half the full height).
What is an apothem?
The apothem is the distance from the center of a regular polygon to the midpoint of one of its sides — it's used together with the perimeter to calculate a regular polygon's area.
How do I calculate area for an L-shaped room?
Split the room into two rectangles along the inside corner, calculate each rectangle's area separately, then add them together for the total.
Does the area formula change for a 3D shape's surface?
Yes — that's surface area, calculated by summing the area of each face of the 3D shape, which is a different calculation from both a flat 2D area and the shape's volume.