1 1/2 inches to mm

1 1/2 inches (1.5 inch) × 25.4 = 38.1 mm. Reverse: 38.1 ÷ 25.4 = 1.5 in.

Use the converter at the top. Type a decimal or a fraction (1/16, 3 1/2). Millimeters update from the same engine as the inch to mm hub (1 in = 25.4 mm).

1. Write the length as a decimal inch if needed: 1 1/2 in = 1.5 in (1.5 inch).
2. Multiply by 25.4: 1.5 × 25.4 = 38.1 mm.
3. Optional centimeters: divide millimeters by 10 → 3.81 cm.

The nearest metric size is 38 mm, 0.1 mm smaller than 38.1 mm.

38 mm is 0.1 mm smaller than 38.1 mm and 40 mm is 1.9 mm larger. Those are the metric dowel and hole sizes people compare with 1 1/2 in (1.5 in). Neither is exact. A nominal “1 1/2 inch pipe” is a trade size, not a 1.5 in outside diameter.

1 1/2 inches is 38.1 mm, not a whole millimeter. Whole-millimeter neighbors:

• 38 mm is 0.1 mm smaller than 1 1/2 inches.
• 39 mm is 0.9 mm larger than 1 1/2 inches.

1 1/2 inches as a length is 38.1 mm (1.5 × 25.4). That is the conversion on this page — a cut, a wrench opening, or a mark on a stick.

A nominal 1-1/2 inch PVC or waste pipe is a trade size (NPS), not an outside diameter of 1.5 in. ASME B36.10M lists the NPS 1-1/2 outside diameter as 1.900 in, which is 48.26 mm — 10.16 mm larger than 38.1 mm. Inside diameter is smaller than that OD and depends on wall schedule, so it is not 38.1 mm either. Measure the actual OD or ID, then multiply inches by 25.4.

A 1-1/2 inch wrench opening is the same 38.1 mm as this length. A 38 mm wrench is 0.1 mm smaller; a 40 mm wrench is 1.9 mm larger. Neither metric opening is an exact 1-1/2 in substitute.

On a millimeter ruler, 38.1 mm sits just past the 38 mm tick (38 mm is 0.1 mm short of 1 1/2 in).

For the 1 in = 25.4 mm definition as a short lesson, see the video on mm to inches — not a pipe-size video. YouTube already occupies two slots on this query; this page keeps the hardware diagram on-page.