Outer faces and curved surfaces
Surface Area Calculator
Choose a three-dimensional shape to find its outside surface area. See total area and the surfaces included in your result.
Enter your measurements
Two ways to measure area
Choose a flat shape or a solid. Both use square units, but they measure different surfaces.
Flat shapes
Find the area of a single flat shape. Use length units such as feet or meters for every dimension.
Surface area of solids
Add up the outer faces or curved surfaces of a three-dimensional shape. Choose which faces to include.
Surface area measures the outside of a solid
Surface area is the combined area of the faces or curved surfaces covering a three-dimensional shape. Results use square units, such as ft² or m². Volume measures the space inside and uses cubic units.
Rectangular box
A = 2(LW + LH + WH)
For a cube with side s, A = 6s². Leave out LW for an open top.
Cylinder
A = 2πrh + 2πr²
The curved side is 2πrh. Each circular end adds πr².
Triangular prism
A = PL + 2T
P is the triangle perimeter, L the prism length and T the area of one triangular end.
Cone
A = πrs + πr²
s is slant height. Exclude πr² to leave out the base.
Sphere
A = 4πr² = πd²
The full curved surface has four times the area of a circle with the same radius.
Example: a closed box
A box with length 4 ft, width 3 ft and height 2 ft has surface area 2 × (4 × 3 + 4 × 2 + 3 × 2) = 52 ft², or approximately 4.83 m².
Which surfaces should be included?
For a closed solid, include every outer face. For a container without a lid, leave out its opening. The cylinder tool lets you choose zero, one or two end caps. The cone tool can leave out its base.
This is an ideal geometric surface estimate. Painting both sides, wall thickness, seams, overlaps, cuts and material waste need separate allowances. Use outside dimensions when measuring the outer surface.
Enter every length in the same unit. Results are rounded for display; calculations use unrounded values and the full precision of π.