+1 digital calipers

Measure them yourself several times to verify consistency and then use 2 different spoke length calculators to see if you get the same result. Finding out you bought the wrong length spokes would be very frustrating.

Here are a couple wheel building references:

https://www.parktool.com/blog/calvin...e-rim-diameter

Spoke Calculator: https://kstoerz.com/freespoke/