If you plan to use a silo for storage space for grain, you should calculate how much space you have available in total. A silo is a relatively cylindrical shape with a halfdome on top, so you can use the formulas for the volume of a sphere and a cylinder to determine how much storage space you have in your silo.
Things You'll Need
 Stepladder
 Flexible tape measure
 Nail
 Calculator

Attach the bottom of the tape measure to the base of the silo. Climb up to the top, lay the tape measure against the wall and note the measurement.

Find the center point of the silo's interior and measure from it to any point on a wall. This gives you the radius.

Multiply pi, or 3.14, by the square of the radius to calculate surface area. Multiply the surface area by the height of the cylindrical portion of the silo to determine that area. A silo with a radius of 10 feet and a height of 20 feet for the cylinder has a volume of 6,280 cubic feet.

Determine the area of the dome portion of the silo with the sphere volume formula: (4/3)(pi)(r^3). Divide the result by 2 to find the formula for the area of a dome. The result should be 2,093.32 cubic feet.

Add the two portions. The result should be 8,373.32 cubic feet.
References
 Photo Credit silo image by andreaschneider from Fotolia.com