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Reading guide
Worked example2 3/8 in = 2.375 in = 60.325 mm
| Reading | Equivalent | How to read it |
|---|---|---|
| 1/16 in | 1.5875 mm | One smallest interval |
| 1/4 in | 6.35 mm | Four smallest intervals |
| 3/8 in | 9.525 mm | Six smallest intervals |
| 1 in | 25.4 mm | Sixteen intervals |
Read the hierarchy of inch marks
There are sixteen small intervals in each inch on this scale. The halfway mark is 8/16, or 1/2 inch. Quarter marks are 4/16 and 12/16; eighth marks are every two intervals. Reduce the numerator and denominator to name a fraction: six small intervals are 6/16 = 3/8 inch. Add the whole inches before the fraction to obtain the full reading.
A fraction is not always an exact match
The reading helper shows the nearest sixteenth and its rounding difference in millimeters. A decimal input such as 0.3 inch falls between marked ticks; rounding it to 5/16 changes the length. The blue target guide keeps the entered length, while the helper explains the nearest tick. For fitting parts, keep the original dimension instead of silently substituting a rounded fraction.
Can this show a full 12-inch ruler?
Only if twelve physical inches fit within the calibrated measuring span. Fullscreen can recover browser space, but cannot make the screen larger. A phone cannot display a twelve-inch scale at actual size. For a longer object, use a suitable physical ruler or tape measure. Our printable ruler provides a verified 10-inch PDF; it is not compressed into a pretend 12-inch scale.
How this ruler works
The scale uses your current calibration in CSS pixels per inch. Metric ticks divide that density by 25.4; inch ticks divide it by 16. Conversions use the exact definition 1 inch = 25.4 mm. The target keeps its entered length rather than stretching to fill the display.
Keep browser zoom at 100%, verify with a known reference, and recheck after changing screens. Inputs stay in your browser; no camera, account, or upload is required. For critical dimensions, use a suitable calibrated physical instrument.
Methodology, calibration help, and measurement support: Accuracy methodology · Calibrate screen · Contact us. Unit definitions: NIST.