Use this free online surface area calculator to find the total surface area of a cube, rectangular box, sphere, cylinder, or cone. Pick your shape, enter its dimensions, and get an accurate surface area result instantly.
How to Use the Surface Area Calculator
Select your "Shape" - cube, rectangular box, sphere, cylinder, or cone.
Enter the required dimensions for that shape (e.g. Side for a cube, Length/Width/Height for a box, Radius for a sphere, or Radius and Height for a cylinder or cone).
Click "Calculate" to compute the surface area.
Review the "Surface Area" result shown below the button.
Formulas and Sample Results
Surface area is the total area of every face or curved surface that encloses a solid. The calculator uses the standard textbook formula for each shape and rounds the answer to 3 decimal places. Using the placeholder values from the form, you should see these results:
Shape
Total surface area
Sample input
Result
Cube
6a²
a = 3
54
Rectangular Box
2(lw + lh + wh)
5 × 4 × 3
94
Sphere
4πr²
r = 3
113.097
Cylinder
2πr² + 2πrh
r = 3, h = 5
150.796
Cone
πr² + πrl
r = 3, h = 5
83.23
For the cone, the Height field means the vertical height from the centre of the base to the tip, not the slant height. The tool finds the slant height l = √(3² + 5²) ≈ 5.831 itself, giving a base area of about 28.274 and a curved area of about 54.955.
Total vs Curved Surface Area in Real Jobs
This tool always returns the total surface area, including every base and lid. Many practical jobs need only part of it, so adjust the figure before buying material:
Painting the walls of a room 4 m long, 3.5 m wide and 3 m high: the box result is 73 m², but that includes the floor and ceiling (14 m² each). The four walls alone are 2 × (4 × 3 + 3.5 × 3) = 45 m², before deducting doors and windows.
Coating a cylindrical tank with radius 0.6 m and height 1.2 m: the total is about 6.786 m², but if the bottom sits on a slab and only the side and lid are coated, use 2πrh + πr² ≈ 5.655 m².
For an open pipe or a tin with no lid, keep only the curved part 2πrh, plus one πr² if it has a base.
Common Mistakes
Entering the diameter instead of the radius. Halve the diameter first, otherwise the area comes out four times too large.
Mixing units. Enter every dimension in the same unit. The answer is in that unit squared, so metres give m² and centimetres give cm². One square metre equals 10,000 cm² and about 10.764 sq ft.
Typing the slant height of a cone into the Height box. If you only know the slant height l, the vertical height is √(l² − r²).
The calculator does not convert units. The result is in the square of whatever unit you typed, so dimensions in feet give square feet and dimensions in metres give square metres.
For a cylinder with radius = 3 and height = 5, the surface area is 2π(3²) + 2π(3)(5) = 2π(9) + 2π(15) ≈ 56.549 + 94.248 ≈ 150.796 square units.
The cone's slant height is calculated as √(radius² + height²) using the Pythagorean theorem, then used in the lateral surface area term π r × slant height, which is added to the base area π r² for the total surface area.
Calculate the sphere with the same radius and halve it to get the curved surface 2πr². For a solid hemisphere with a flat circular face, add πr², giving 3πr² in total. With r = 3 that is about 84.823.