Copper Pipe Size Converter
Convert between copper pipe nominal sizes, actual outer diameters, wall thickness, and inner diameters for Type K, L, and M tubing.
Select a nominal pipe size and type to see all dimensions, or enter a measurement to find the matching size.
Underground lines: Type K (thickest walls)
Actual OD = Nominal size + 1/8 inch
Understanding Copper Pipe Sizing
Copper pipe (more accurately called copper tubing) is sized by its nominal diameter, which does not match the actual outer diameter (OD). The nominal size is always 1/8 inch less than the actual OD. For example, a 1/2 inch nominal copper pipe has an actual outer diameter of 5/8 inch (0.625 inches or 15.88 mm).
The Three Main Types:
Copper tubing comes in three standard types defined by wall thickness. The outer diameter stays the same for a given nominal size, but the wall thickness and therefore the inner diameter differ between types.
| Type | Color Code | Wall Thickness | Common Use |
|---|---|---|---|
| Type K | Green | Thickest walls | Underground, high pressure |
| Type L | Blue | Medium walls | Interior plumbing, most common |
| Type M | Red | Thinnest walls | Low-pressure residential |
Key Formulas:
Actual OD (inches) = Nominal size + 1/8 inchInner diameter = Outer diameter - (2 × wall thickness)OD in mm = OD in inches × 25.4
Common Copper Pipe Dimensions:
| Nominal Size | Actual OD (in) | Actual OD (mm) | Type L Wall (in) | Type L ID (in) |
|---|---|---|---|---|
| 1/4" | 0.375 | 9.53 | 0.030 | 0.315 |
| 3/8" | 0.500 | 12.70 | 0.035 | 0.430 |
| 1/2" | 0.625 | 15.88 | 0.040 | 0.545 |
| 3/4" | 0.875 | 22.23 | 0.045 | 0.785 |
| 1" | 1.125 | 28.58 | 0.050 | 1.025 |
| 1-1/4" | 1.375 | 34.93 | 0.055 | 1.265 |
| 1-1/2" | 1.625 | 41.28 | 0.060 | 1.505 |
| 2" | 2.125 | 53.98 | 0.070 | 1.985 |
Practical Examples:
- A standard home water supply line uses 3/4 inch Type L copper tubing with an actual OD of 0.875 inches (22.23 mm) and an inner diameter of 0.785 inches (19.94 mm).
- For a bathroom sink, 1/2 inch Type M copper is common, with an actual OD of 0.625 inches (15.88 mm) and wall thickness of only 0.028 inches.
- Underground water mains use Type K because its thicker walls resist soil pressure and corrosion better than Type L or M.
Tips:
- Always match fittings to the copper type you are using, as solder joint depth can vary.
- Copper tubing sold in straight lengths (hard temper) is different from coiled tubing (soft temper).
- The nominal size system applies only to North American copper tubing standards (ASTM B88). European and metric systems use actual OD measurements directly.