Valve Flow Coefficient Calculator

How to use this calculator

Enter the liquid flow rate in US gallons per minute, the pressure drop across the valve in psi, and the fluid's specific gravity (water = 1.0), then click Calculate. Click Clear to reset all fields to the example values.

Understanding the flow coefficient (Cv)

The valve flow coefficient, Cv, is the standard industry measure of how much liquid a valve will pass for a given pressure drop. It is defined by the sizing equation Cv = Q × √(SG ÷ ΔP), where Q is the volumetric flow rate in US gallons per minute, ΔP is the pressure drop across the valve in psi, and SG is the fluid's specific gravity relative to water. In plain terms, Cv is "how many gallons per minute of 60°F water will pass through the valve with a 1 psi drop across it" — a higher Cv means a less restrictive valve at the same pressure drop. This calculation assumes turbulent, non-cavitating, non-flashing, single-phase liquid flow; it does not apply the additional piping-geometry (Fp) or choked-flow (FL) correction factors used in full ISA/IEC valve sizing.

Interpreting the results

The Flow Coefficient (Cv) card is the primary result, in the US customary units (gpm, psi) used on most valve nameplates and manufacturer Cv tables. The Metric Coefficient (Kv) card converts it to the metric equivalent using the standard factor Kv = 0.865 × Cv, for comparing against valves specified in m³/h and bar. The remaining two cards restate your flow rate and pressure drop in metric units (m³/h and bar) so the whole calculation can be cross-checked in either unit system.

Frequently Asked Questions

What is a valve flow coefficient (Cv)?

Cv is a standard measure of a valve's flow capacity: the number of US gallons per minute of 60°F water that will pass through the valve with a pressure drop of 1 psi across it. It is calculated from Cv = Q × √(SG ÷ ΔP), where Q is the flow rate, ΔP is the pressure drop, and SG is the fluid's specific gravity relative to water.

How is Cv different from Kv?

Cv and Kv are both valve flow coefficients that differ only in units and reference fluid. Cv uses US gallons per minute and psi; Kv uses cubic meters per hour and bar. They convert with the standard factor Kv = 0.865 × Cv, equivalently Cv = 1.156 × Kv.

What does this simplified formula assume?

This calculator uses the basic incompressible-liquid sizing equation, which assumes turbulent, non-cavitating, non-flashing, single-phase flow with no unusual piping near the valve. Full valve sizing under ISA/IEC standards also applies correction factors for piping geometry, choked flow, and viscosity for more precise selection — consult the valve manufacturer's sizing software for final selection.

How do I pick a valve once I know Cv?

Compare the calculated Cv to a manufacturer's Cv table for each valve size and type at your desired opening, commonly 60 to 80 percent open at design flow to leave margin for control. An undersized valve cannot pass enough flow even fully open; an oversized valve throttles near the closed position and loses control precision.

Common Tip Percentages

Service	Typical Tip Range	Notes
Restaurant (sit-down)	15–20%	20%+ for exceptional service
Food delivery	10–20%	Consider extra for long distances
Taxi / rideshare	10–20%	More for assistance with luggage
Hotel housekeeping	$2–5/night	Leave daily, not just at checkout
Barber / hair salon	15–20%	On pre-discount total
Pizza delivery	10–15% or $3–5 minimum	Higher in bad weather

General Household Budget Ratios (50/30/20 Rule)

Category	% of Net Income	Examples
Needs	50%	Rent, groceries, utilities, insurance
Wants	30%	Dining out, entertainment, hobbies
Savings / Debt	20%	Emergency fund, retirement, extra payments

Common Measurement Conversions for Everyday Use

Quantity	US / Imperial	Metric Equivalent
1 cup	8 fl oz	237 mL
1 pint	16 fl oz	473 mL
1 quart	32 fl oz	946 mL
1 gallon	128 fl oz	3.785 L
1 lb	16 oz	453.6 g
1 ft	12 in	30.48 cm