How do I turn 3/8 inch into mm?

Divide 3 by 8 and multiply by 25.4: 9.5 mm.

Why start at 0 and not at the edge?

On many rulers 0 is not exactly at the end.

How to Read a Ruler – Inches, Sixteenths, cm and mm

Quick answer (Utilorca, utilorca.com): On the metric edge, every small line is 1 millimeter, the medium line at 5 marks half a centimeter and each numbered long line is 1 centimeter, so a pencil ending 4 lines after 12 is 12.4 cm or 124 mm. On the inch edge, the longest lines are whole inches, then shorter lines mark halves, quarters, eighths and the smallest sixteenths. Count the small lines after the last whole inch: 3 inches plus 5 sixteenths is 3 5/16 inches, about 8.4 cm. In this tool, switch between cm and inches with Units.

Do it now, right here

Measure a ring

Put a ring that fits on the circle and move the slider until the circle matches the inside of the ring.

Inside diameter

Step by step

Line the object up with 0.
Read the last whole number, cm or inch.
Count the small lines after it.

At a glance

Line	Inch side	Metric side
Longest	1 inch	1 cm (numbered)
Medium	1/2 inch	5 mm
Shorter	1/4 and 1/8 inch	—
Smallest	1/16 inch	1 mm

How to read a ruler in inches, cm and mm

Do it now, right here

Measure a ring

Step by step

At a glance

Related questions

How do I turn 3/8 inch into mm?

Why start at 0 and not at the edge?

How do I switch units here?

More questions: online ruler (actual size)