Pipe Diameter Flow Rate Chart
Interactive flow rate charts and capacity tables for standard pipe sizes. Select pipe material and design velocity to generate a complete flow capacity reference.
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Flow rate chart summaryClick "Generate Chart" to create a pipe diameter flow rate table.
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Schedule 40 pipe sizes, water flow in GPM and LPM at four design velocities, and recommended velocities by application. One PDF, made to pin above the bench.
How It Works
The Pipe Diameter Flow Rate Chart uses the fundamental continuity equation to calculate the volumetric flow rate through pipes of various standard sizes at specified velocities. This provides a quick reference for pipe sizing and system design.
Flow Rate Equation
The volumetric flow rate is calculated using the continuity equation:
Q = V × A = V × π/4 × D²
Where:
- • Q = Volumetric flow rate
- • V = Fluid velocity
- • A = Pipe cross-sectional area
- • D = Actual inside diameter of the chosen material, not the nominal size
Recommended Design Velocities
Typical velocity ranges for common applications:
| Application | Imperial (ft/s) | Metric (m/s) |
|---|---|---|
| Domestic Cold Water | 4 – 8 | 1.2 – 2.4 |
| Domestic Hot Water | 3 – 5 | 0.9 – 1.5 |
| Commercial Water | 4 – 10 | 1.2 – 3.0 |
| Fire Protection | 10 – 15 | 3.0 – 4.6 |
| Cooling Water | 5 – 10 | 1.5 – 3.0 |
| Steam (Low Pressure) | 60 – 100 | 18.3 – 30.5 |
| Compressed Air | 20 – 30 | 6.1 – 9.1 |
Standard Pipe Sizes Reference (Schedule 40 Steel)
Nominal Pipe Size (NPS) and the actual inside diameters of Schedule 40 steel pipe (ASME B36.10). Other materials have other bores for the same nominal size: 1/2" Type L copper is 0.545" and 1/2" Schedule 40 PVC averages 0.609". Pick the material above and the chart uses its own bores. PVC figures are the average bore makers publish (minimum wall plus 6%), so one maker's pipe can differ slightly.
| NPS | DN | Actual ID (in) | Actual ID (mm) |
|---|---|---|---|
| 1/2" | DN15 | 0.622 | 15.80 |
| 3/4" | DN20 | 0.824 | 20.93 |
| 1" | DN25 | 1.049 | 26.64 |
| 1-1/4" | DN32 | 1.380 | 35.05 |
| 1-1/2" | DN40 | 1.610 | 40.89 |
| 2" | DN50 | 2.067 | 52.50 |
| 2-1/2" | DN65 | 2.469 | 62.71 |
| 3" | DN80 | 3.068 | 77.93 |
| 4" | DN100 | 4.026 | 102.26 |
| 6" | DN150 | 6.065 | 154.05 |
| 8" | DN200 | 7.981 | 202.72 |
| 10" | DN250 | 10.020 | 254.51 |
| 12" | DN300 | 11.938 | 303.23 |
FAQ
Here you will find the answers to the frequently asked questions about pipe diameter flow rate charts.
Frequently Asked Questions
What size pipe do I need for my flow rate?
Use the chart above and select a design velocity appropriate for your application. For domestic water supply, use 4-8 ft/s (1.2-2.4 m/s). Find the pipe size in the chart where the flow rate at your chosen velocity meets or exceeds your required flow. Always round up to the next standard pipe size to allow for future capacity and pressure drop considerations.
What is the maximum flow rate for a 1-inch pipe?
The maximum flow rate for a 1-inch Schedule 40 pipe (actual ID 1.049 inches) depends on the velocity. At 5 ft/s, flow is approximately 13 GPM. At 8 ft/s, flow is approximately 22 GPM. At 10 ft/s, flow reaches approximately 27 GPM. For most domestic water applications, 13-22 GPM is the practical maximum to avoid noise and excessive pressure drop.
What is a safe water velocity in pipes?
For most water piping applications, 4-8 ft/s (1.2-2.4 m/s) is considered safe. Velocities above 10 ft/s (3 m/s) can cause excessive noise, pipe vibration, and accelerated erosion, particularly at fittings and direction changes. Very low velocities below 2 ft/s can lead to sediment buildup. Fire protection systems may use higher velocities of 10-15 ft/s due to their intermittent operation.
How does pipe material affect flow capacity?
Material changes the inside diameter for a given nominal size, and that changes capacity. A 1/2-inch Type L copper tube has a 0.545-inch bore, against 0.622 inches for 1/2-inch Schedule 40 steel, so at 5 ft/s the copper carries about 3.6 GPM and the steel about 4.7 GPM. Pick the material above and the chart uses that material's own bores. Material also sets the internal roughness, represented by the Hazen-Williams C-factor: smoother pipe such as copper and PVC (C=150) loses less pressure than old cast iron (C=100). Roughness changes the pressure needed to drive the flow, not the capacity at a given velocity, so it does not change this chart.
What is the difference between nominal and actual pipe size?
Nominal Pipe Size (NPS) is a standardized label that does not correspond to any physical dimension of the pipe. For example, a 1-inch NPS Schedule 40 pipe has an actual internal diameter of 1.049 inches. The actual internal diameter varies by wall thickness (schedule). Higher schedules have thicker walls and smaller internal diameters. Always use the actual internal diameter, not the nominal size, when calculating flow rates.
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