NPS, DN, Schedule 40/80, OD & ID

Pipe Size Chart

Pipe size is usually listed by nominal pipe size (NPS) or DN, not by the exact measured diameter. For example, NPS 1/2 pipe is commonly mapped to DN 15 and has an outside diameter of 0.840 in.

Use this chart to compare NPS, DN, outside diameter, inside diameter, wall thickness, and Schedule 40 / Schedule 80 values. The outside diameter stays fixed for the same NPS, while the inside diameter changes with schedule and wall thickness.

For pressure-rated, code-regulated, fuel gas, fire protection, structural, or other safety-critical work, verify the applicable material standard, pressure class, local code, and manufacturer data, or consult a qualified professional.

NPS & DNNominal size designations
OD & IDOutside vs inside diameter
Schedule 40/80Wall thickness and ID
PrintableReference chart

Pipe size quick lookup

Start with the nominal size, then check the measured outside diameter and the schedule-specific wall thickness or inside diameter. These common examples show why the name of a pipe size is not the same as its measured diameter.

NPS 1/2
DN 15 · OD 0.840 in

ID changes by schedule. Use the chart row before using an inside-diameter value.

NPS 1
DN 25 · OD 1.315 in

A common small-pipe reference. DN 25 is not 25 mm OD.

NPS 2
DN 50 · OD 2.375 in

Use OD for outside-fit checks. Use schedule for wall thickness and ID.

Schedule 40 vs 80
Same OD · different wall and ID

For the same NPS, Schedule 80 generally has a thicker wall and smaller ID than Schedule 40.

Use the chart as a dimension reference

The table compares nominal pipe size, DN, outside diameter, schedule, wall thickness, inside diameter, and weight. Use it for quick reference, printing, shop planning, and measurement checks. Do not use a dimension chart alone as the final specification for regulated or pressure-rated work.

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Residential Plumbing • 1/2 → 8 • A4

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Pipe Size Chart

Standard: NPS • Range: 1/2 - 8 • A4

NPSDNODScheduleWallIDWeight
1/2DN 150.840" / 21.3mmSCH 400.109" / 2.77mm0.622" / 15.76mm0.85 lb/ft / 1.27 kg/m
1/2DN 150.840" / 21.3mmSCH 800.147" / 3.73mm0.546" / 13.84mm1.09 lb/ft / 1.62 kg/m
3/4DN 201.050" / 26.7mmSCH 400.113" / 2.87mm0.824" / 20.96mm1.13 lb/ft / 1.69 kg/m
3/4DN 201.050" / 26.7mmSCH 800.154" / 3.91mm0.742" / 18.88mm1.48 lb/ft / 2.20 kg/m
1DN 251.315" / 33.4mmSCH 400.133" / 3.38mm1.049" / 26.64mm1.68 lb/ft / 2.50 kg/m
1DN 251.315" / 33.4mmSCH 800.179" / 4.55mm0.957" / 24.30mm2.17 lb/ft / 3.24 kg/m
1-1/4DN 321.660" / 42.2mmSCH 400.140" / 3.56mm1.380" / 35.08mm2.27 lb/ft / 3.39 kg/m
1-1/4DN 321.660" / 42.2mmSCH 800.191" / 4.85mm1.278" / 32.50mm3.00 lb/ft / 4.47 kg/m
1-1/2DN 401.900" / 48.3mmSCH 400.145" / 3.68mm1.610" / 40.94mm2.72 lb/ft / 4.05 kg/m
1-1/2DN 401.900" / 48.3mmSCH 800.200" / 5.08mm1.500" / 38.14mm3.63 lb/ft / 5.41 kg/m
2DN 502.375" / 60.3mmSCH 400.154" / 3.91mm2.067" / 52.48mm3.66 lb/ft / 5.44 kg/m
2DN 502.375" / 60.3mmSCH 800.218" / 5.54mm1.939" / 49.22mm5.03 lb/ft / 7.48 kg/m
2-1/2DN 652.875" / 73.0mmSCH 400.203" / 5.16mm2.469" / 62.68mm5.80 lb/ft / 8.63 kg/m
2-1/2DN 652.875" / 73.0mmSCH 800.276" / 7.01mm2.323" / 58.98mm7.67 lb/ft / 11.41 kg/m
3DN 803.500" / 88.9mmSCH 400.216" / 5.49mm3.068" / 77.92mm7.58 lb/ft / 11.29 kg/m
3DN 803.500" / 88.9mmSCH 800.300" / 7.62mm2.900" / 73.66mm10.26 lb/ft / 15.27 kg/m
3-1/2DN 904.000" / 101.6mmSCH 400.226" / 5.74mm3.548" / 90.12mm9.12 lb/ft / 13.57 kg/m
3-1/2DN 904.000" / 101.6mmSCH 800.318" / 8.08mm3.364" / 85.44mm12.52 lb/ft / 18.63 kg/m
4DN 1004.500" / 114.3mmSCH 400.237" / 6.02mm4.026" / 102.26mm10.80 lb/ft / 16.07 kg/m
4DN 1004.500" / 114.3mmSCH 800.337" / 8.56mm3.826" / 97.18mm15.00 lb/ft / 22.32 kg/m
5DN 1255.563" / 141.3mmSCH 400.258" / 6.55mm5.047" / 128.20mm14.63 lb/ft / 21.77 kg/m
5DN 1255.563" / 141.3mmSCH 800.375" / 9.53mm4.813" / 122.24mm20.80 lb/ft / 30.97 kg/m
6DN 1506.625" / 168.3mmSCH 400.280" / 7.11mm6.065" / 154.08mm18.99 lb/ft / 28.26 kg/m
6DN 1506.625" / 168.3mmSCH 800.432" / 10.97mm5.761" / 146.36mm28.60 lb/ft / 42.56 kg/m
8DN 2008.625" / 219.1mmSCH 400.322" / 8.18mm7.981" / 202.74mm28.58 lb/ft / 42.55 kg/m
8DN 2008.625" / 219.1mmSCH 800.500" / 12.70mm7.625" / 193.70mm43.43 lb/ft / 64.64 kg/m

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File Details

Rows

26

Range

1/2 → 8 • A4

PDF FILE SIZE

≈0KB

Quality

300 DPI

How to read a pipe size chart row

Read across one row in this order: nominal size first, outside diameter next, then schedule-specific wall thickness and inside diameter.

  1. 1

    Find the nominal size

    Find the NPS or DN size class. NPS and DN are nominal designations. They name the size class; they are not exact measured diameters.

  2. 2

    Check outside diameter

    Use the OD column for fittings, clamps, hangers, sleeves, and wall penetrations.

  3. 3

    Select the schedule

    Choose the schedule to compare wall thickness and read the corresponding inside diameter. For the same NPS, a thicker wall means a smaller inside diameter.

  4. 4

    Confirm the specification

    Verify material, pressure class, manufacturer data, applicable standard, and local code requirements before final specification.

Common pipe size examples

These examples are useful because the nominal size can look smaller than the measured outside diameter, especially in common NPS sizes below 14.

NPS 1/2 pipe

NPS 1/2 pipe is commonly mapped to DN 15 and has an outside diameter of 0.840 in. The inside diameter depends on the selected schedule.

NPS 1 pipe

NPS 1 pipe is commonly mapped to DN 25 and has an outside diameter of 1.315 in. DN 25 is a nominal designation, not a 25 mm outside diameter.

NPS 2 pipe

NPS 2 pipe is commonly mapped to DN 50 and has an outside diameter of 2.375 in. Check Schedule 40, Schedule 80, or the required schedule before using wall thickness or inside diameter.

These examples show why nominal pipe size is not the same as measured outside diameter. Always use the schedule row when you need wall thickness or inside diameter.

Key pipe size definitions

Use these definitions before comparing rows. The most common mistake is treating a nominal label as a measured diameter.

NPS
Nominal Pipe Size. An inch-based size designation, not an exact outside or inside diameter. Example: NPS 2 has an OD of 2.375 in, not 2.000 in.
DN
Diameter Nominal. A metric nominal designation used internationally. It is not an exact measured millimeter diameter; for example, DN 25 corresponds to NPS 1 and about 33.4 mm OD, not 25 mm OD.
OD
Outside diameter. This is the measured outside width of the pipe and is often the value used for fittings, clamps, hangers, sleeves, and holes.
ID
Inside diameter. This changes with schedule and wall thickness, even when the NPS and OD stay the same.
Schedule
A wall thickness series, such as Schedule 40 or Schedule 80. Schedule changes wall thickness and inside diameter; it does not change the OD for the same NPS.
Wall thickness
The pipe wall measurement. For the same OD, a thicker wall leaves a smaller inside diameter.

Schedule 40 vs Schedule 80 pipe

For the same NPS, Schedule 40 and Schedule 80 generally use the same outside diameter. Schedule 80 usually has a thicker wall, so its inside diameter is smaller than Schedule 40.

Schedule is a wall thickness series. It helps compare wall thickness and inside diameter, but it is not the full engineering specification. Pressure suitability depends on pipe material, temperature, joining method, corrosion allowance, applicable standard, manufacturer rating, and local code requirements.

  • Same NPS: OD stays fixed.
  • Higher schedule: thicker wall in common comparisons.
  • Thicker wall: smaller ID and smaller flow area.
  • Final selection: confirm standard, material, pressure class, manufacturer data, and code requirements.

Safety note

This chart is a general dimension reference. Do not use it as the only source for pressure-rated, fuel gas, fire protection, structural, or code-regulated installations. Verify the material standard, pressure class, manufacturer data, and local code requirements, or consult a qualified professional.

Related engineering and measurement charts

After you identify the pipe size, these charts can help with related measurement tasks such as pressure unit conversion, fractional clearances, material density, and workshop layout references.

Fraction → DecimalEducational
FractionDecimalPercent
1/640.01561.56%
1/320.03133.13%
1/160.06256.25%
1/80.125012.5%
3/160.187518.8%
1/40.250025%
5/160.312531.3%
3/80.375037.5%
1/20.500050%
3/40.750075%

Fraction to Decimal

Use this when pipe clearances, holes, sleeves, or field measurements are written as inch fractions.

View chart
Material DensityEngineering
Materialkg/m³SG
Water10001.00
Aluminum27002.70
Steel78507.85
Gold1932019.3
Oak7000.70
Pine4200.42
Concrete24002.40
Glass25802.58
PVC13801.38
Gasoline7200.72

Material Density Chart

Use this for material or fluid density references when a project needs a separate weight or density lookup.

View chart
PSI → BarEngineering
PSIBarkPa
100.6969
201.38138
302.07207
322.21221
352.41241
402.76276
503.45345
604.14414
805.52552
1006.89689

PSI to Bar Chart

Use this for pressure unit conversion only; it does not replace pipe pressure-rating verification.

View chart
Lumber SizesWorkshop preset
NominalActual Size
1 x 23/4" x 1 1/2"
1 x 33/4" x 2 1/2"
1 x 43/4" x 3 1/2"
2 x 41 1/2" x 3 1/2"
2 x 61 1/2" x 5 1/2"
2 x 81 1/2" x 7 1/4"
4 x 43 1/2" x 3 1/2"
4/413/16"
8/41 3/4"
3/4" Ply23/32"

Lumber Size Chart

Use this for workshop material size planning when pipe layout connects to framing, boards, or shop fixtures.

View chart

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Frequently Asked Questions

Common questions about pipe sizing, NPS, DN, outside diameter, inside diameter, and schedule.

Is pipe size the same as outside diameter?+
No. Pipe size is usually a nominal label. The outside diameter is fixed for each NPS, while the inside diameter changes depending on schedule and wall thickness.
What is the OD of 1/2 inch pipe?+
NPS 1/2 pipe has an outside diameter of 0.840 in and is commonly mapped to DN 15. Its inside diameter depends on the schedule, so check the Schedule 40, Schedule 80, or required schedule row before using an ID value.
What is NPS 2 outside diameter?+
NPS 2 pipe has an outside diameter of 2.375 in and is commonly mapped to DN 50. The outside diameter stays fixed for NPS 2, while wall thickness and inside diameter change by schedule.
What is DN in pipe size charts?+
DN means Diameter Nominal. It is a metric nominal designation, not an exact measured millimeter diameter. For example, DN 25 corresponds to NPS 1 and about 33.4 mm OD, not 25 mm OD.
How do I convert NPS to DN?+
Use DN as the metric nominal size that corresponds to the NPS size class. Common examples are NPS 1/2 = DN 15, NPS 1 = DN 25, and NPS 2 = DN 50. Then use the chart to confirm OD, wall thickness, inside diameter, and schedule.
Does Schedule 40 change pipe OD?+
No. For the same NPS, Schedule 40 and Schedule 80 generally use the same outside diameter. Schedule changes wall thickness, which changes the inside diameter and flow area.
Why does inside diameter change for the same NPS?+
Inside diameter changes because the outside diameter is fixed for the NPS while wall thickness changes by schedule. A thicker wall leaves less inside space, so the ID becomes smaller.
What is the difference between Schedule 40 and Schedule 80 pipe?+
For the same NPS, Schedule 80 generally has a thicker wall than Schedule 40, so Schedule 80 has a smaller inside diameter. Pressure suitability still depends on material, temperature, manufacturer rating, standard, and code requirements.
Which column should I use for fittings and clamps?+
Use outside diameter (OD) for fittings, clamps, hangers, sleeves, and wall penetrations. Use inside diameter (ID) and schedule only after the schedule is selected, then confirm the applicable material and specification requirements.
Can I use this pipe size chart for plumbing or pressure-rated work?+
Use this chart as a general dimension reference only. For plumbing, pressure-rated systems, fuel gas, fire protection, structural work, or other regulated installations, verify the material standard, pressure class, manufacturer data, and local code requirements, or consult a qualified professional.
What is STD and XS?+
STD means Standard, and XS means Extra Strong. In many common pipe-size ranges, STD often matches Schedule 40 and XS often matches Schedule 80, but exact relationships vary by size and standard. Check the chart and the applicable specification before relying on those labels.
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