Plumbing · New

Pipe Sizing Calculator

Determine the correct pipe diameter based on flow rate, pressure, material, and run length.

Flow + runSupply line

Flow rate

GPM

Pipe material

Total run length

Max velocity

RecommendedLIVE

Sample data

Example numbers for a 1–2 person shop. Edit any field to make it yours — it saves on this device.

Minimum pipe size

COPPER pipe

Flow velocity

3.89 fps

Friction loss

0.03 ft

Pressure drop

0.01 psi

Status

Suitable

Flow rate10 GPM

Run length50 ft

MaterialCOPPER

Velocity limit8 fps

Sized to velocity

1" COPPER carries 10 GPM at 3.89 fps — inside your 8 fps limit and above the 1 fps minimum.

velocity = 0.4085 × GPM ÷ ID²

friction = 10.44 × (GPM/C)^1.852 ÷ ID^4.87 (per 100ft)

pressure = friction(ft) × 0.433

All options

Every size for 10 GPM in COPPER.

Size	Velocity (fps)	Friction (ft)	Status
1"	3.89	0.03	Suitable
2"	1.04	0	Suitable
3"	0.47	0	Too slow
4"	0.27	0	Too slow
1/2"	13.75	0.76	Too fast
3/4"	6.63	0.13	Suitable
1-1/4"	2.55	0.01	Suitable
1-1/2"	1.8	0.01	Suitable
2-1/2"	0.67	0	Too slow

Field notes

Pipe sizing fundamentals.

Balance velocity and cost

Too small and velocity climbs — noise, water hammer, erosion, pressure loss. Too large wastes material and money. The sweet spot is the smallest size that stays under your velocity cap.

Velocity guidelines

Residential (quiet): 4–5 fps
Standard: 5–8 fps
Commercial mains: up to 10 fps
Never exceed 10 fps

Material matters

PEX and PVC run smoother (higher C-factor), so they have less friction than copper at the same ID. Copper is more rigid and better for exposed runs.

Hot water & CPVC

CPVC handles hot water better than PVC but has a slightly smaller internal diameter at the same nominal size — which nudges velocity up. Size with that in mind.

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