About

TowingMath is a small set of free towing and trailer weight calculators, built by Allen App Tools in Spokane, Washington.

How these are built

Every calculator on this site shows the formula it uses, works an example through by hand, and links the standard or regulation the figures come from. Where a number is an industry convention rather than a specification - hitch class ratings, for instance - the page says so rather than presenting it as settled.

The arithmetic runs entirely in your browser. Nothing you type is sent anywhere, because there is no server to send it to. The whole site is static files.

How the maths is checked

Each calculator has automated tests that load the actual published page and drive the real calculator, asserting against hand-computed values. The worked example printed on a page and the number the calculator returns are verified to agree, because a worked example that disagrees with the tool is worse than having neither.

What this site does not do

It does not replace weighing your rig, and it does not override your manufacturer. Towing limits are set by the vehicle and trailer makers and printed on the door placard and VIN plate. When a calculation here is close to a limit, the right answer is to weigh the rig and take the more conservative number.

This is not professional or engineering advice. See the disclaimer.

Corrections

If you find an error in a formula, a figure or a source, it should be fixed. Accuracy on a site about load limits is the whole product.