What GPM means
GPM means gallons per minute, the flow rate of water through a pipe, fixture, pump or nozzle.
Also called gallons per minute, flow rate.
Where it matters on a plumbing job
Tankless water heaters, well pumps, irrigation zones and pressure washers are all sized by GPM. Measure flow before you quote equipment that depends on it, since a weak supply limits everything after it.
What the model code says
- The code's maximum flow for a shower head is 2.5 gpm at 80 psi. (IRC 2021, Chapter 29)
Check which code edition your building department enforces for GPM before you quote.
What it costs
Koira's tankless water heater installation cost guide puts a typical job at $2,750, with most between $1,400 to $3,950. The guide shows its sources and what moves the price. The water pipe sizing calculator prices a job line by line.
Work it out
- Free calculator: Water pipe sizing calculator
- Cost guide: Tankless water heater installation cost
- Licensing: Plumbing license rules by state
- Tools, templates and guides: Free plumbing resources
Sources: 2021 International Residential Code, Chapter 29, Water Supply and Distribution (ICC). Checked October 9, 2026.