Trying to figure out how to measure and cut certain dimensions

[bigboy1991]

I have came up with the design of my box using subbox pro. The confusion comes when the cuts I'm suppose to be making are numbers like 18.21x 20.50, 18.96x20.50, 34.37x20.50 .ect. How do I even measure such odd numbers. 20.50 is easy because i see it on the tape measure but 34.37 has me thinking "where is this on the tape measure". I'm probably overthinking it but my brain hurts trying to figure this out lol

 

[Joe X]

You can set the dimensions of your design to dimensions you can work with even if your volume and other box specs go slightly off, your parts should assemble perfectly or your box will not be structurally sound and air leaks may develop.