I've made a little of calculations considering the IFOV of the Flir Lepton that is 6,2:
At 10 Meters the spot you can mesure is 62 mm x 62 mm, but Flir advise to multiply for 3 to maximize the precision so is 186 mm x 186 mm
At 10 Meters the spot you can mesure is 2,44" x 2,44" , but Flir advise...