Water Supply Curve Calculator

Enter your hydrant flow test — static, residual, and test flow — and it plots the supply curve and tells you the available flow at any pressure you choose.

What it does

Using the standard Hazen-Williams supply-curve relationship, the tool draws the pressure-vs-flow curve and computes:

• Available flow at your chosen residual pressure (e.g., 20 psi): Q₂ = Q₁ × ((Ps − P₂) / (Ps − Pr))^0.54
• The maximum flow where the curve reaches 0 psi
• A plotted curve with the static, residual, and target points marked

How to use it

1. Enter static pressure, residual pressure, and the test flow (gpm).
2. Enter the pressure you want to read available flow at (defaults to 20 psi).
3. Read the available flow and the plotted curve.

FAQ

What method does it use?

The standard 1.85 power-law (Hazen-Williams) water-supply curve used throughout fire sprinkler hydraulics.

Is it on mobile?

Yes — it's part of the free SprinkFlow mobile app, so you can read a curve right at the hydrant.