4 mm is about 0.157 inches, or about 5/32 inch (slightly more). Divide millimeters by 25.4, because 1 inch is defined as exactly 25.4 mm.
4 mm ≈ 5/32″
Slightly more than 5/32″ (by 0.03 mm) · ≈ 0.157 in
- Inches
- ≈ 0.1575 in
- Nearest 1/16″
- 3/16″ 4 mm is 0.76 mm shorter
- Nearest 1/32″
- 5/32″ 4 mm is 0.03 mm longer
- Nearest 1/64″
- 5/32″ 4 mm is 0.03 mm longer
How big is 4 mm?
4 mm = 4 ÷ 25.4 in ≈ 0.15748 in. On a tape measure that is 10/64 in, which reduces to 5/32 in (0.15625 in), and 4 mm is longer than that by about 0.03 mm. In other metric units, 4 mm is exactly 0.4 cm and exactly 0.004 m.
Compared with other common fractions: 1/8 in is 3.175 mm, so 4 mm is about 0.83 mm more; 3/16 in is 4.7625 mm, so 4 mm is about 0.76 mm less.
Things that are about 4 mm
These are nominal sizes. Real parts vary a little with the maker, so check the part when fit matters.
An M4 screw
The “M4” label means a thread diameter of 4 mm, common in electronics, laptops and small appliances.
A 4 mm hex (Allen) key
4 mm is a standard metric hex key size. The nearest inch size, 5/32 in (3.97 mm), is a bit smaller and can round off a bolt if it is loose. Use the exact size when you can.
A 4 mm drill bit
A standard metric bit size. The closest fraction bit, 5/32 in, drills a hole about 0.03 mm smaller.
4 mm thick board
Plywood, hardboard and acrylic are sold in 4 mm thickness. It is a bit thicker than 1/8 in (3.175 mm) and a bit thinner than 3/16 in (4.76 mm).
A 4 mm bead
4 mm is a small round bead size used in jewelry and crafts, a little over 1/8 of an inch across.
A 4 mm connector
Banana plugs and some electrical terminals are made in 4 mm sizes. Check the product specification, because the 4 mm refers to the pin or hole diameter.
Nearby millimeter sizes
Decimals are rounded to 3 places. In the fraction columns, + means the value is slightly longer than the fraction, − slightly shorter, and = exact.
| Millimeters (mm) | Inches (decimal) | Nearest 1/16″ | Nearest 1/32″ |
|---|---|---|---|
| 1 mm | 0.039 | 1/16″ − | 1/32″ + |
| 2 mm | 0.079 | 1/16″ + | 3/32″ − |
| 3 mm | 0.118 | 1/8″ − | 1/8″ − |
| 4 mm | 0.157 | 3/16″ − | 5/32″ + |
| 5 mm | 0.197 | 3/16″ + | 3/16″ + |
| 6 mm | 0.236 | 1/4″ − | 1/4″ − |
| 7 mm | 0.276 | 1/4″ + | 9/32″ − |
| 8 mm | 0.315 | 5/16″ + | 5/16″ + |
| 9 mm | 0.354 | 3/8″ − | 11/32″ + |
| 10 mm | 0.394 | 3/8″ + | 13/32″ − |
| 11 mm | 0.433 | 7/16″ − | 7/16″ − |
| 12 mm | 0.472 | 1/2″ − | 15/32″ + |
Frequently asked questions
How many inches is 4 mm?
4 mm is about 0.157 inches (0.15748 in), or about 5/32 inch, slightly more.
Is 4 mm the same as 5/32 inch?
Almost. 5/32 inch is 3.96875 mm, so 4 mm is about 0.03 mm longer. For most everyday uses they are treated as the same size.
How many cm is 4 mm?
4 mm is exactly 0.4 cm, because 1 cm is 10 mm.
Is 4 mm the same as 1/8 inch?
No. 1/8 inch is 3.175 mm, so 4 mm is about 0.83 mm larger.
Is 4 mm the same as 3/16 inch?
No. 3/16 inch is 4.7625 mm, so 4 mm is about 0.76 mm smaller.
How do I convert mm to inches?
Divide the millimeters by 25.4. For 4 mm, 4 ÷ 25.4 ≈ 0.157 inches.