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SimuPipe

Pipe Sizing Calculator

Find the optimal pipe size for your flow conditions. Enter a flow rate and fluid, then set velocity or pressure drop limits to see which pipe sizes are suitable.

Fluid
Density998.2 kg/m³
Viscosity1.002 cP
Pipe & Flow
Constraints
ResultsRecommended: NPS 5"
Display:
NPSDNID (mm)Velocity (m/s)dP (kPa)dP/L (kPa/100m)ReRegimeStatus
1/8"66.875.761391759.91391759.9515,802Turbulent
1/4"89.241.37280529.2280529.2381,183Turbulent
3/8"1012.522.5656680.956680.9281,442Turbulent
1/2"1515.814.1716745.216745.2223,072Turbulent
3/4"2020.98.073864.33864.3168,387Turbulent
1"2526.64.981108.51108.5132,270Turbulent
1-1/4"3235.12.88272.2272.2100,544Turbulent
1-1/2"4040.92.11124.5124.586,181Turbulent
2"5052.51.2835.5135.5167,127Turbulent
2-1/2"6562.70.89914.6814.6856,197Turbulent
3"8077.90.5825.045.0445,225Turbulent
3-1/2"9090.10.4352.472.4739,107Turbulent
4"100102.30.3381.341.3434,464Turbulent
5" Best fit125128.20.2150.4480.44827,492Turbulent
6"150154.10.1490.1850.18522,877Turbulent
8"200202.70.0860.0500.05017,385Turbulent
10"250254.50.0550.0170.01713,847Turbulent
12"300303.20.0380.007290.0072911,623Turbulent
14"350333.30.0320.004650.0046510,572Turbulent
16"400381.00.0240.002470.002479,250Turbulent
18"450428.70.0190.001410.001418,222Turbulent
20"500477.80.0150.0008430.0008437,376Turbulent
24"600574.60.0110.0003530.0003536,133Turbulent

How it works: For each pipe size in the selected schedule, the calculator computes velocity and pressure drop using Darcy-Weisbach with Colebrook-White friction factor. The smallest pipe that satisfies your constraints is recommended. Pipe roughness is based on the selected material (0.0450 mm).

How to Size a Pipe

Pipe sizing is the process of selecting the correct pipe diameter for a given flow rate, fluid, and set of constraints. The two most common criteria are:

  • Maximum velocity — keeping fluid velocity below recommended limits prevents erosion, noise, and water hammer. Typical limits are 1.5-3 m/s for water and 15-25 m/s for gases.
  • Maximum pressure drop — a pressure drop constraint (usually expressed as kPa per 100m) ensures the system can deliver the required pressure at the endpoint. Common limits range from 0.5-2 kPa/100m for gravity systems to 5+ kPa/100m for pumped systems.

This calculator uses the Darcy-Weisbach equation with the Colebrook-White implicit friction factor to compute pressure loss for each available pipe size in the selected schedule. The Reynolds number determines whether the flow is laminar or turbulent.

For full pipe network analysis with multiple branches, pumps, valves, and control devices, try SimuPipe — our browser-based pipe network simulation tool.

Frequently Asked Questions

How do I choose the right pipe size?
Pipe sizing is a balance between velocity, pressure drop, and cost. Higher velocities mean smaller (cheaper) pipes but more pressure drop and noise. A common approach is to set a maximum velocity limit (e.g. 2-3 m/s for water, 20-30 m/s for gas) or a maximum pressure drop per unit length, then find the smallest standard pipe size that meets the criteria.
What is a good flow velocity for water pipes?
For general industrial water service, 1.5-3 m/s is typical. Suction lines to pumps should be slower (0.5-1.5 m/s) to avoid cavitation. Fire water mains can run up to 4-5 m/s during emergencies. Higher velocities increase erosion risk and water hammer. For chilled water and HVAC systems, 1-2.5 m/s is common to limit noise and pump energy.
What velocity should I use for compressed air?
For compressed air headers, 6-10 m/s is recommended to limit pressure drop. Branch lines can run up to 15 m/s. Distribution mains in large plants should stay below 8 m/s. Higher velocities cause excessive pressure drop and can carry condensate moisture further into the system. Always check that the total pressure drop is within your system's allowance.
What is the maximum allowable pressure drop?
There is no single answer — it depends on the system. For process piping, a rule of thumb is 0.1-0.5 bar per 100 m of pipe. For compressed air, total system losses should stay under 10% of compressor discharge pressure. For pump suction lines, the available NPSH sets the limit. This calculator lets you evaluate pressure drop for each candidate pipe size to find the best fit.
Why does pipe schedule matter for sizing?
Pipe schedule determines wall thickness and therefore internal diameter. A thicker wall (higher schedule) means a smaller bore for the same nominal size, which increases velocity and pressure drop. For example, NPS 4 Schedule 40 has an ID of 102.3 mm, while Schedule 80 has 97.2 mm. This calculator uses pipe schedule data to compute the actual internal diameter for accurate sizing.

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