u003cstrongu003eA: u003c/strongu003eWhen measuring for your truck toolbox, the most important number to get right is the length of the box. The outside length of the toolbox must measure slightly less than the inside width of your truck bed, or the under mounting space that you plan to use. If you use larger tools, be sure to measure the inside length and width of the toolbox to ensure that it will be able to accommodate your larger tools.