DO NOT base your choice on your trouser size.
Take a string or tape measure and measure snugly where you plan to wear your tool belt.
Belts are typically worn on the hips, support the small of the back.
For example, Joel wears a size 33” waist jeans. But measures a 37” around his hips, where he likes to wear his tool belt.Keep in mind your working conditions. If you work outside in all seasons, layers will increase your circumference. But oOur belts have around four or five inches of flexibility for the best fit. This is more than enough for most people.
For an optimal fit, there should be 1" to a max of 6" of open space between your belt ends. see Blue arrow above.
For instance, if your measurement is 36”, you should go with a medium belt which will leave about 3” of open space. Choose what you think will work best for your working conditions.