Enrichment · STEM Explorations · Fluids

How much water
a pipe can carry,
and how fast.

Type the inside diameter and either the speed of the water or the flow. The calculator works out the other, in US and metric units, and how long a tank takes to fill.

Work out the flowWhat you get

The pipe flow calculator

The worked example is a made-up 1 inch barn water line at 5 ft/s filling a 500 gallon tank. Nothing you type leaves this browser.

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What you get

Enrichment · STEM ExplorationsFree

What you finish with
Flow or velocity in US and metric units, the time to fill a tank, and the velocity in other pipe sizes. It prints as a summary and downloads as a spreadsheet.
Who it is for
Physics and engineering students, agriculture and trades students, and families planning a water line or irrigation.
Format
Browser calculator for a phone, tablet or computer, by touch or keyboard. Prints a summary; downloads a spreadsheet (.csv); export and import a file.
Access
Free. No account, no sign-in and nothing to install. Everything you type stays in this browser; nothing is sent to Caveat.
Where it lives
The STEM Explorations space in Caveat Enrichment.
Support
Questions, a correction or a request: team@caveatacademic.com.

How to use it

  1. Type the pipe's inside diameter and its unit.
  2. Type the velocity or the flow, leaving the other blank.
  3. Add a tank size to see the fill time.
  4. Compare pipe sizes in the table.
  5. Print the summary for a project.

Work out the flow

How the flow is worked out

Continuity: area times velocity.

The worked example: a 1 inch lineArea0.785 in²π × 1² ÷ 4× velocity0.772 L/s5 ft/s = 1.524 m/sFlow12.24 gpm46.3 L/min500 gal tank41 min500 ÷ flowThe worked example: a 1 inch lineArea0.785 in²π × 1² ÷ 4× velocity0.772 L/s5 ft/s = 1.524 m/sFlow12.24 gpm46.3 L/min500 gal tank41 min500 ÷ flow
Flow is the area of the pipe times how fast the water moves. Double the diameter and the area, and the flow at the same speed, goes up four times.

The arithmetic

The cross-section of a round pipe is π × diameter² ÷ 4. The volume passing each second is that area times the average velocity of the water. Rearranged, velocity is flow ÷ area. Converting: 1 ft = 0.3048 m, 1 US gallon = 3.785411784 L, 1 m³ = 1,000 L.

In practice

Nominal pipe sizes are names, not inside diameters; a 1 inch pipe can be 0.8 to 1.05 inches inside depending on material and schedule. Friction lowers flow over long runs, which this page does not model. Velocities above about 8 ft/s are noisy and can cause water hammer.

Sources

  1. National Institute of Standards and Technology. Handbook 44, appendix C: the US gallon and the foot (nist.gov).
  2. OpenStax. College Physics 2e, section 12.1: flow rate and its relation to velocity (openstax.org).
  3. U.S. Geological Survey. Water science school: how streamflow and flow rate are measured (usgs.gov).
  4. U.S. Department of Agriculture, Natural Resources Conservation Service. National Engineering Handbook, irrigation pipeline design (nrcs.usda.gov).

The worked example is made up. Check inside diameters for your pipe material. Your figures stay in this browser. Support: team@caveatacademic.com.