Check the tire sidewall for the wheel size marking
Look for markings such as 26 x 1.95, 27.5 x 2.1, 700 x 35C, or 29 x 2.25
Read the ISO/ETRTO number on the tire, such as 37-622
Measure the wheel diameter from bead seat to bead seat if markings are missing
Measure the tire width if you need the full wheel and tire size
Match the wheel size to the frame and fork clearance
Verify the rim diameter and tire compatibility before buying
Use a tape measure if you need to confirm size manually
Compare the measurement to standard bike wheel sizes
Check the owner’s manual or manufacturer specifications for the bike model