What Is the Pipe-Fitting Formula for a 45-Degree Offset?

The pipe-fitting formula for a 45-degree offset in plumbing is the length of a diagonal connector, known as the travel, times 0.707. To calculate rolling offset, when a pipe changes direction both vertically and horizontally, it is necessary to find the values for true offset, the setback and the diagonal.

True offset is found by squaring the offset and adding the square of the rise value to equal the true offset squared. The square root is then found to determine true offset. With true offset determined, a pre-existing table can be used to find setback and diagonal values.

Plumbing often involves working on pipes hidden behind walls, in small utility rooms or in other tight spaces. Plumbers often work without direct access to pipes, for instance when working with underground sewer lines. In some cases, cameras are sent in to assess problems, and then plumbers use pumps lowered with cables to execute pipe replacements.

Understanding some math, especially geometry, is necessary for plumbers who must calculate exact angles for pipes and their fittings. The Pythagorean theorem is used in plumbing to find the value for true offset. The theorem holds that in a right triangle, the square of the side opposite the right angle equals the sum of the squares of the other two sides.