The information here is provide as a general guide. Please use common sense.
Our sizes are set mainly on waist size, since most tree planters want to carry the load on their hips. To do this, the belt must be tight enough, and padding should not distort to much or pack out. Our belts are measure to the minimum size, so they can fit larger people, but not smaller.
Waist belts: small (red): >=26", medium (yellow): >=32", large (green): >=36". Note that this is the belt minimum, but smaller waist is possible with padding...
Shovel size is more variable and relative to tree-planting itself. A d-handle shovel should not be long enough to drag when carrying it. This will cause problems for the planter and may lead to lost time from repetitive use injury, or at the very least it may cause sore shoulders. To get an idea of your size measure from your palm to the ground with a straight arm.
If you are planting in fast easy ground short is usually most efficient.
Handles/shaft and blade sizes include the functional measurements. So, while a blade can measure 7" the functional size may be 16" to add with handle of 9" just for example would give you a 25" shovel.