Area Formulas Printable Reference
Use this reference to choose the correct area formula before opening the live geometry calculators. Area measures surface coverage, so results are interpreted in square units.
Printable focus
7 formulas
Covers core shapes plus notes for parallelograms and compound areas, with direct paths to the live geometry calculators.
Common area formulas
Rectangle and square
A = length x width
For a square, length and width are the same side value, so the formula can also be written as A = s^2.
Triangle
A = (base x height) / 2
Height must be perpendicular to the chosen base. A slanted side is not automatically the height.
Circle
A = pi x r^2
Radius is the distance from the center to the edge. If you know diameter, divide it by two first.
Trapezoid
A = ((base A + base B) / 2) x height
Average the two parallel bases, then multiply by the perpendicular distance between them.
How to choose the right area formula
Area is a two-dimensional measurement. That means it answers how much surface a shape covers, not how far it is around the edge. The result should be written in square units such as square inches, square centimeters, square feet, or square meters. Before using any formula, confirm that all dimensions use the same measurement unit.
Rectangles and squares are the simplest area problems because their sides meet at right angles. Triangles use half of a matching rectangle or parallelogram, so the base-height product is divided by two. Circles use pi and radius squared, which is why confusing diameter with radius creates a large error. Trapezoids average the two parallel bases before multiplying by height.
Parallelogram area is base times perpendicular height, similar to a rectangle that has been shifted sideways. Compound shapes should be split into smaller rectangles, triangles, circles, or trapezoids, then added or subtracted. For example, an L-shaped floor plan can usually be split into two rectangles. A shaded region may require subtracting a smaller circle or rectangle from a larger shape.
Live Calculators