Calculator inputs
Formula used
Standard DN and NPS values use a lookup relationship. Outside diameter comes from the selected standard size. Inside diameter equals outside diameter minus twice wall thickness.
Flow area: A = π × ID² ÷ 4
Millimetres to inches: inches = millimetres ÷ 25.4
How to use this calculator
Choose a conversion direction and enter the known size. Select a schedule when wall data is required. Submit the form, then review and export your results.
- Choose DN-to-NPS or NPS-to-DN conversion.
- Enter a standard, decimal, or fractional size.
- Select the schedule, standard, material, and precision.
- Enable dimension calculations when wall data is needed.
- Copy, print, share, or download the calculated result.
DN, NPS, and actual diameter
DN identifies a standardized nominal pipe size. NPS expresses the matching nominal size in inches. Neither value always equals the measured outside diameter exactly.
Schedule changes wall thickness for a selected nominal size. The outside diameter usually remains fixed within that series. Always confirm dimensions against the governing project standard first.
Example conversions
Examples demonstrate that nominal sizes are not direct measurements. DN 50 corresponds to NPS 2, not 1.969 inches. Use the lookup before specifying real pipe components safely.
| DN | NPS inches | NPS decimal | Outside diameter |
|---|---|---|---|
| DN 15 | 1/2 | 0.500 | 21.3 mm |
| DN 50 | 2 | 2.000 | 60.3 mm |
| DN 100 | 4 | 4.000 | 114.3 mm |
| DN 300 | 12 | 12.000 | 323.9 mm |
DN to NPS reference table
| DN | NPS decimal | NPS fraction | OD mm | OD inches |
|---|---|---|---|---|
| DN 6 | 0.125 | 1/8 | 10.3 | 0.406 |
| DN 8 | 0.250 | 1/4 | 13.7 | 0.539 |
| DN 10 | 0.375 | 3/8 | 17.1 | 0.673 |
| DN 15 | 0.500 | 1/2 | 21.3 | 0.839 |
| DN 20 | 0.750 | 3/4 | 26.7 | 1.051 |
| DN 25 | 1.000 | 1 | 33.4 | 1.315 |
| DN 32 | 1.250 | 1 1/4 | 42.2 | 1.661 |
| DN 40 | 1.500 | 1 1/2 | 48.3 | 1.902 |
| DN 50 | 2.000 | 2 | 60.3 | 2.374 |
| DN 65 | 2.500 | 2 1/2 | 73.0 | 2.874 |
| DN 80 | 3.000 | 3 | 88.9 | 3.500 |
| DN 90 | 3.500 | 3 1/2 | 101.6 | 4.000 |
| DN 100 | 4.000 | 4 | 114.3 | 4.500 |
| DN 125 | 5.000 | 5 | 141.3 | 5.563 |
| DN 150 | 6.000 | 6 | 168.3 | 6.626 |
| DN 200 | 8.000 | 8 | 219.1 | 8.626 |
| DN 250 | 10.000 | 10 | 273.0 | 10.748 |
| DN 300 | 12.000 | 12 | 323.9 | 12.752 |
| DN 350 | 14.000 | 14 | 355.6 | 14.000 |
| DN 400 | 16.000 | 16 | 406.4 | 16.000 |
| DN 450 | 18.000 | 18 | 457.2 | 18.000 |
| DN 500 | 20.000 | 20 | 508.0 | 20.000 |
| DN 550 | 22.000 | 22 | 558.8 | 22.000 |
| DN 600 | 24.000 | 24 | 609.6 | 24.000 |
| DN 650 | 26.000 | 26 | 660.4 | 26.000 |
| DN 700 | 28.000 | 28 | 711.2 | 28.000 |
| DN 750 | 30.000 | 30 | 762.0 | 30.000 |
| DN 800 | 32.000 | 32 | 812.8 | 32.000 |
| DN 850 | 34.000 | 34 | 863.6 | 34.000 |
| DN 900 | 36.000 | 36 | 914.4 | 36.000 |
| DN 950 | 38.000 | 38 | 965.2 | 38.000 |
| DN 1000 | 40.000 | 40 | 1016.0 | 40.000 |
| DN 1050 | 42.000 | 42 | 1066.8 | 42.000 |
| DN 1100 | 44.000 | 44 | 1117.6 | 44.000 |
| DN 1150 | 46.000 | 46 | 1168.4 | 46.000 |
| DN 1200 | 48.000 | 48 | 1219.2 | 48.000 |
Calculation history
Frequently Asked Questions
1. What does DN mean in pipe sizing?
DN means Diameter Nominal within metric pipe identification. It labels a standard size rather than exact measurement. The number supports matching components across recognized piping systems.
2. What does NPS mean?
NPS means Nominal Pipe Size in inch-based systems. It provides a standardized name for compatible pipe dimensions. Actual outside diameter can differ from the nominal label.
3. Is DN measured in millimetres?
DN uses metric-style numbers associated with millimetres. However, DN remains a nominal designation, not direct measurement. Always check the listed outside diameter before final selection.
4. Can DN be divided by 25.4?
Direct division does not reliably produce the correct NPS. DN and NPS use coordinated standardized lookup categories. Use the reference table for dependable nominal size matching.
5. Why is DN 50 called a two-inch pipe?
DN 50 maps to NPS 2 by convention. Its outside diameter is approximately 60.3 millimetres. Nominal names describe compatibility rather than measured diameter alone.
6. Is NPS the pipe's actual diameter?
NPS is not usually the measured outside diameter. Smaller sizes show especially noticeable differences from nominal values. Consult outside diameter data before designing joints or supports.
7. Does pipe schedule change NPS?
Schedule does not change the selected nominal pipe size. It primarily changes wall thickness and inside diameter. Matching NPS components generally retain their established outside diameter.
8. Does schedule change outside diameter?
Schedule normally keeps outside diameter fixed for that NPS. A thicker wall reduces the available internal flow diameter. Verify special products because some dimensional series differ significantly.
9. How is inside diameter calculated?
Inside diameter uses outside diameter and wall thickness. Subtract twice the wall thickness from outside diameter. This method requires valid schedule data for accurate results.
10. Are DN and NPS values standardized?
DN and NPS values follow recognized dimensional systems. Exact available sizes depend on product and governing standard. Confirm every critical selection using current approved project documentation.
11. Can this calculator be used for PVC pipes?
The nominal conversion can support preliminary PVC comparisons. Plastic pipes may use different outside diameter series. Check manufacturer dimensions before ordering fittings or pipe materials.
Limitations and engineering notice
This calculator supports planning and educational comparisons. Schedule data is unavailable for some nominal size combinations. Verify final dimensions using approved standards and manufacturer documentation.