Calculate valve Kv coefficient from flow rate and pressure drop.
About this calculatorThis calculator determines the valve Kv coefficient needed for a given flow rate and allowable pressure drop. Kv represents the flow in cubic meters per hour of water at a 1-bar pressure drop. Use it when selecting control valves to ensure the valve provides the required flow capacity at the design pressure drop for the hydronic circuit.
Use whenYou need to determine the required valve Kv for a known flow and pressure drop.
FormulaKv = Q × √(SG ÷ ΔP)
Variables
UnitsMetric (m³/h, bar) or Imperial (GPM, PSI)Flow RateFlow rate in m³/h or GPMΔPPressure drop in bar or PSI
Metric (m³/h, bar)
Measurement system for flow and pressure
Design flow rate through the valve
Allowable pressure drop across the valve
Required Kv—
Recommended Kvs (×1.3)—
What is valve Kv?
Kv is the flow coefficient used internationally to express a valve's flow capacity. It is defined as the flow rate in cubic meters per hour (m³/h) of water at 5–40°C that produces a pressure drop of 1 bar across the valve. Kv is calculated from the relationship: Kv = Q × √(SG ÷ ΔP), where Q is the flow rate in m³/h, SG is the specific gravity of the fluid relative to water, and ΔP is the pressure drop in bar. A higher Kv indicates a larger valve or more open flow path. When selecting control valves for hydronic HVAC systems, the design Kv should typically allow the valve to operate between 50% and 80% open at design conditions, leaving travel available for control above and below the design point. Valve authority (the ratio of valve pressure drop to total circuit pressure drop) should be at least 0.3–0.5 for stable control.
