What size pipe is a 5 inch circumference?

Answer 1

The formula for working out the circumference of a circle (like a pipe) is diameter times pi. (You should find pi on your calculator, if not, it is 3.14159265) Since you know the circumference, you divide the circumference (5inch) by pi (3.14159265), and you get the diameter, i.e. the size pipe.

While the above formulas are correct, using this equation example will not tell you what size pipe you have. There are a number of factors involved in determining the correct answer. There are many different materials that pipe is made out of and some of these affect the dimensions of the pipe. As an example, the actual outside diameter of 1" copper pipe and 1" steel pipe are not the same. If you are talking about steel pipe, it is important to understand that all pipe 12 inch and under is referred to as "nominal" pipe size. In this case, the outside diameter of 12 inch pipe is actually 12.75 inches. For the original question asked above, the 5 inch circumference would equal 1-9/16" outside diameter which would be the equivalent of 1-1/4" pipe (nominal).