See explanation if you are measuring using a rollout test. This calibration number is different from the one for kilometers for most of these cyclocomputers..

700 X 44

1382

700 X 38

1355

700 X 35

1347

700 X 32

1339

700 X 28

1327

700 X 25

1308

700 X 23

1302

700 X 20

1296

27 X 1 3/8

1349

27 X 1 1/4

1343

27 X 1 1/8

1339

27 X 1

1333

26 X 2.125

1286

26 X 1.9

1276

26 X 1.5

1234

26 X 1.25

1213

26 X 1.0 (559 mm)

1189

26 x 1 (650C)

1213

Wide 700C Tubular

1316

Narrow 700C Tubular

1308

26 X 1 3/8

1288

24

1191

24 x 1

1089

20 X 1.75 (406)

927

20 X 1 1/4 (451)

1005

17 x 1 1/4

838

16 x 1 3/8

797

These computers don't adjust their internal math -- instead, you change the calibration number. A mile is 1.6093 kilometers, and the calibration number for miles is the tire circumference divided by 1.6093. You can measure the tire circumference with a rollout test, then do the division.

The manual for the Vetta Cycle computer gives the calibration number for miles as 3.9042 times the radius of the wheel. This is the same as the circumference divided by 1.6093.