Surface Area Calculator
Calculate the surface area of a cube, sphere, cylinder, or cone.
Splits the total into base and lateral area, and converts to square metres and square feet.
Surface area is the total area of every outer face of a three-dimensional shape. It is measured in square units (cm², m², in², ft²) and it is the number behind almost every material estimate: paint, wrapping, insulation, plating, packaging.
This tool covers four shapes. Enter one dimension for a cube or sphere, two for a cylinder or cone.
Cube (side length s): SA = 6s² Example: a cube with 4 cm sides gives SA = 6 × 16 = 96 cm²
Sphere (radius r): SA = 4πr² Example: a sphere with r = 6 cm gives SA = 4 × π × 36 = 452.4 cm²
Cylinder (radius r, height h): SA = 2πr² + 2πrh, which is top plus bottom plus the wrapped side Example: r = 3 cm and h = 10 cm gives 56.5 + 188.5 = 245.0 cm²
Cone (radius r, vertical height h): SA = πr² + πrl, where the slant l = √(r² + h²) Example: r = 4 cm and h = 7 cm gives a slant of 8.06 cm, so 50.3 + 101.3 = 151.6 cm²
Height or slant? The cone trap
This is where cone calculations go wrong, and the two numbers are never the same. The vertical height h runs straight up the middle from the centre of the base to the tip. The slant l runs up the outside along the surface, and it is always the longer of the two because it is the hypotenuse of a triangle whose legs are h and r.
Enter the VERTICAL height here. The calculator squares it, adds r², takes the root and uses that as the slant. If you type a slant into the height box you will get an answer that is too big, by 25% on a wide shallow cone. Feed in r = 4 with a genuine slant of 7 and the honest total is 138.2 cm², not the 151.6 above.
Worked example: how much paint for a room? Room: 4 m × 5 m, 2.5 m high, two coats on the walls only. Wall area = 2(4 × 2.5) + 2(5 × 2.5) = 20 + 25 = 45 m² Two coats = 90 m² Coverage varies a lot between products, so read the figure off the tin. At the 10 m² per litre that emulsion often quotes, that is 9 litres.
Why surface area matters:
- Packaging design, where the goal is the least material for a given volume
- Heat exchange, since a larger surface cools or heats faster
- Drug delivery, where a tablet’s surface area sets how fast it dissolves
- Construction estimating for paint, render, cladding and insulation
How we build and check this calculator
This calculator runs entirely in your browser, so the numbers you enter stay on your device. The math behind it is written by hand and tested against worked examples and standard references before the page goes live.
SuperGlobalCalculator is independently built and maintained. See how we build and verify our calculators.