Water Pressure Calculator
PSI from head height & friction
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Water source height above outlet
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Formula & explanation
Water pressure from gravity (static head) is 0.433 psi per vertical foot of drop. Friction loss depends on pipe length, diameter, flow rate, and fittings — this calculator gives a rough estimate using a simplified loss factor. Real systems must also account for elbows, valves, elevation changes, and the actual flow demand.
Example calculation
50 ft of head, 100 ft of 3/4\" pipe:
Static pressure = 50 × 0.433 = 21.65 psi. Friction loss ≈ 100 × (0.5/(0.5625)) ≈ 1.3 psi → ~20.3 psi dynamic at the outlet.
Buying & project-planning tips
- Typical home water pressure is 40–80 psi — below 30 is weak; above 80 may damage fixtures and requires a regulator.
- Friction loss grows quickly in small pipes at high flow — oversizing pipes reduces pressure drop.
- Pressure regulators (PRVs) protect fixtures when municipal supply exceeds 80 psi.
- Fittings (elbows, valves) add equivalent length — count them for a more accurate loss estimate.
- Well systems use a pressure tank and switch — typically set 30/50 or 40/60 psi cut-in/cut-out.
Frequently asked questions
What is good water pressure for a house?+
40–80 psi is ideal. Below 30 psi feels weak; above 80 psi can damage fixtures and pipes and requires a pressure-regulating valve.
How do I increase low water pressure?+
First identify the cause — undersized supply, clogged pipes, a failing pressure regulator, or a weak well pump. A plumber can diagnose; solutions include pipe upsizing, a new PRV, or a booster pump.
Does pipe size affect pressure?+
Yes — smaller pipes cause more friction loss at the same flow. Oversizing supply lines reduces pressure drop, especially over long runs or at high demand.
What's the difference between static and dynamic pressure?+
Static pressure is with no water moving. Dynamic (working) pressure is what's left after friction loss when water flows — what your fixtures actually see in use.
Safety notice: This water pressure estimate is for planning only and does not replace evaluation by a licensed plumber. Pressure, pipe sizing, backflow prevention, and scald prevention are health- and safety-critical — always verify against local plumbing code.