You will need
• ruler, calculator, rope
Instruction
1
If the barrel has a cylindrical shape, measure its height and radius. For thick-walled it is necessary to measure the inner radius to obtain its capacity and not just volume. Translate the results of the measurements to meters. Then use the formula to calculate volume of a cylinder:

Vцил = π * R2 * H,

where:

R is the radius of the base (bottom) of the barrel,
H – height of the barrel,
Vцил – the volume of the cylindrical barrel,
π is the number PI, approximately equal to 3.14.
2
If the radius of the barrel is difficult to measure, then measure its diameter. To do this, clamp one end of a line or rope on the edge of the barrel. Then, turning the ruler or a rope, find the most distant point on the opposite edge. Since the barrel diameter is twice its diameter, the formula to calculate the volume of the barrel will be similar to:

Vцил = π * (D/2)2 * H,

or:

Vцил = ¼ * π * D2 * H
where: D – inner diameter of the bottom of the barrel.
3
If the barrel diameter cannot be measured, then determine the length of its circumference. To do this, take a sufficiently long rope (cord, string, thread, etc.) and wrap it once around the barrel.
Since the circumference is π * D, the barrel diameter will be equal to the length of its circumference divided by π. I.e. D = L / π. To determine the volume of the barrel through the circumference, substitute this expression into the previous formula:

Vцил = ¼ * π * D2 * H = ¼ * π * (L/π)2 * H = ¼ * L2/π * H

where: L – the circumference (girth) of the barrel.
4
If you want to calculate the volume of a classical (pot-bellied) barrels, it is not necessary to examine the composition of Kepler's "Stereometry of wine barrels". Just use the purely practical formula is derived for several centuries winemakers of France:

Vб = 3,2 * r * R * H,

where:

r is the radius of the bottom of the barrel, and
R is the radius of its widest part.

Accordingly, if only the diameters of the bottom (d) and mid (D) of the barrel, then use the formula:

Vб = 0,8 * d * D * H.