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Pressure Reducing Valve (PRV) Sizing Calculator

Calculate the flow coefficient (Cv) needed to select a pressure reducing valve for a given flow rate and pressure drop.

Computed in your browser — nothing you enter is uploaded. Figures are presented for United States against IRC 2024, and every formula is cited under regulatory standards below.

Last verified 2026-08-27 · v1.1.0

Market
Imperial · sales tax

Required flow coefficient (Cv)

11.18 Cv

Check your inputs

This is the standard simplified Cv equation for water service — always confirm the selected valve's actual rated Cv from the manufacturer's catalog at your specific operating conditions before final selection.

For the dimensions entered, expect a required flow coefficient (cv) of 11.2. Moderate confidence — sound arithmetic, but allow for the variation any real site introduces. Set for United States against IRC 2024. The market selector changes both the units and the code cited.

Add the equipment this sizes

This result is a specification — 11.18 Cv — not a quantity. Put the thing it sizes into your project: how many, what you call it, and your supplier’s price.

Preliminary estimate, not certified engineering. This tool produces an indicative quantity calculation for planning purposes only — it is not a certified structural analysis, a guaranteed material takeoff, or a substitute for building department approval. Always verify measurements on-site and have a licensed contractor or structural engineer review any load-bearing, code-sensitive, or safety-critical work before purchasing materials or starting construction. Spotted an arithmetic or standards error? Report it to contact@craftquantities.com with your inputs — confirmed fixes become pinned regression tests.

[Schema Verified] Computed in alignment with American Concrete Institute (ACI 318-19) formulas and International Residential Code (IRC 2024) spatial boundaries.

Regulatory standards & verification citations

  • Simplified valve flow coefficient equation for water: Cv = Q ÷ √(ΔP), where Q is flow rate (gpm) and ΔP is the pressure drop across the valve (psi) — the standard method used in valve manufacturers' catalogs to select a valve size for a target flow and pressure drop

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Frequently asked questions

What is Cv and why does it matter for valve selection?
Cv (flow coefficient) is a standard rating used in manufacturers' catalogs that describes how much flow a valve passes for a given pressure drop. Calculating the Cv your application needs lets you pick a valve model/size whose rated Cv meets or exceeds that value.
Why does a larger pressure drop reduce the required Cv?
The equation divides flow rate by the square root of the pressure drop — for the same flow rate, a bigger pressure drop across the valve means the valve doesn't need to be as "open" a flow path to reach that flow, so a smaller Cv (and often a smaller valve) is enough.
Is this simplified equation accurate enough for final valve selection?
It's the standard simplified Cv equation for water service and works well for a first-pass estimate, but you should always confirm the selected valve's actual rated Cv from the manufacturer's catalog at your specific operating conditions before finalizing the selection.