Kettlebell weights are heavy, rounded exercise tools that you hold by an exposed handle and use for swinging exercises. A cheap alternative to purchasing kettlebells from a commercial retailer is to make your own kettlebells. By calculating the diameter of bell needed to create your desired weight, you can then form a mould using a simple inflatable ball, and pour your kettlebell for only the cost of the products that you use to make bells of multiple sizes.

Divide the desired weight by the cubic-foot weight of your concrete of choice, displayed on the bag, to determine the cubic feet of concrete required.

Multiply the result by 1,728 to convert into cubic inches required.

Multiply the volume by 3/4.

Divide the result by pi.

Take the cube root of the result to determine the radius of the ball required.

Multiply the result by 2, and the result of that by pi to determine the circumference desired.

Inflate ball to the desired circumference, wrapping a string around the ball and measuring the length of the string to determine the circumference.

Mix the plaster of Paris according to your brand of choice's recipe.

Cover the exterior of the ball with a layer of plaster, at least 1 inch thick, leaving a slot at the top of the ball open for the insertion of the handle, then leave to dry.

Deflate the ball once the plaster has dried until the ball is deflated enough to be removed out the hole in the top of the plaster mould.

Thread rebar through the pipe piece, using as many pieces as you can fit.

Secure one end of the rebar pieces in a vice, and pull on the opposite end while wearing work gloves to bend the rebar down and underneath the pipe piece.

Repeat for the second side of rebar so that the pipe makes a handle and the rebar is bent underneath the handle.

Mix the concrete according to the recipe for your brand of choice and pour into the ball mould.

Insert the rebar down into the wet concrete, creating a handle for the bell.

Apply wet concrete around the rebar pieces so that the concrete reaches the pipe.

Break the plaster mould off of the bell once the concrete has dried.