Smoothbore
Smoothbore Flow
Estimate flow from tip diameter and nozzle or pitot pressure.
What It Tells You
How much water a smoothbore tip is flowing at a known pressure.
Formula
GPM = 29.7 × d² × √NP
What the Variables Mean
- GPM
- flow gallons per minute
- d
- tip diameter inches
- NP
- nozzle or pitot pressure PSI
Plain-Language Explanation
A larger tip opening passes more water. Raising nozzle pressure also raises flow, but flow changes with the square root of pressure.
Worked Example
Use a ⅞-inch tip at 50 PSI.
- GPM = 29.7 × 0.875² × √50
Fireground Takeaway
Tip size has a strong effect on flow, so confirm the actual tip before setting the pump.
Practice This Formula
Open Reverse Flow and start a Practice Quiz filtered to this topic.
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