To measure a circle's circumference, find the circle's diameter, then multiply the diameter by pi to find the circumference. If you only have the radius, multiply it by two to find the circle's diameter. More » Science Measurements

Popular online geometry calculators are located on websites such as, and These sites help solve geometric equations by computing an answer from values input by a ... More » Math Math Calculators

A tire calculator can be used to determine the height, sidewall thickness, circumference and revolutions per mile of any tire by typing the tire's size rating in. The size rating is a number following the format 285/75R1... More » Vehicles Car Parts & Maintenance Tires, Rims & Wheels

Pitch circle diameter is a term used to describe the centerline diameter of a circular bolt spacing, the diameter of theoretical friction discs that would transmit the same velocity ratio as two meshing gears, or the dia... More »

To determine the area of a circle from its diameter, divide the diameter by two, square it and multiply by π. The formula for calculating the area of a circle is: A = πr2, where r is the radius of the circle. More »

One can calculate the diameter of a circle mathematically if the circumference or the area of the circle is known. If the location of the center of the circle is known, then the circle's diameter can be measured with a r... More » Science Measurements

To calculate a circle's diameter from its circumference, one should divide the circumference by the constant pi, which is an irrational number approximately equal to 3.14159265358979. More »