how to enter my PD information with "inch"?

[glasses lens]

My PD value is 2.5 inches, is that correct? I can't input it to the RX information on Cheap Glasses Online, Prescription Glasses,Prescription Sunglasses. On my prescription there is only a number 2.5 inches written on the PD entry.
how to enter it? and where i can input? Please help me to complete my order, HELP!!

[eyewear]

PD number is in millimeter. If your ruler has only inch, please convert inch into millimeter or provide us.

As a guideline: (1 inch=25.4 mm)
Most *****s' PD's are between 55-69mm / 2.2-2.7 inches
Most kids' PD's are between 42-54mm / 1.6-2.1 inches

[glasses lens]

so, my P D is 2.5 inches on my prescription. does it means 2.5 * 24.5 mm?

is it correct? my math is bad, if the exact PD is 61.5 mm?