Valve Cv (Flow Coefficient) Calculator — Liquid, Gas & Steam | KELOR Valves
ISA S75.01

Calculate the Flow Coefficient (Cv) for any valve based on flow rate, pressure drop, and fluid properties. Supports liquids, gases, and steam with automatic unit conversion. Get an instant recommended valve size and type for your application. All calculations follow ISA S75.01 standard equations.

Input Parameters

Select fluid type and enter operating conditions

Formula: Cv = Q × √(SG / ΔP) — Q = Flow (GPM), SG = Specific Gravity, ΔP = Pressure Drop (PSI)

Results

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Cv Reference Table — Standard Valve Sizes

Typical Cv ranges by valve size for common valve types, including full bore ball valves and butterfly valves.

Valve SizeDNCv RangeGlobeBallButterflyGate
1/2″DN150.1 – 2.50.2 – 2.55 – 20—5 – 15
3/4″DN200.5 – 50.5 – 510 – 40—10 – 30
1″DN252 – 102 – 1020 – 8015 – 5020 – 60
1-1/4″DN324 – 164 – 1635 – 12025 – 8035 – 90
1-1/2″DN406 – 256 – 2550 – 16030 – 12050 – 150
2″DN5010 – 4010 – 4080 – 25050 – 20080 – 300
2-1/2″DN6516 – 5216 – 52130 – 40080 – 300130 – 500
3″DN8025 – 8125 – 81200 – 600120 – 500200 – 700
4″DN10052 – 12052 – 120350 – 1000200 – 900400 – 1200
6″DN150100 – 280100 – 280800 – 2500500 – 2000900 – 3000
8″DN200200 – 500200 – 5001500 – 40001000 – 35001500 – 5000
10″DN250350 – 800—2500 – 60001500 – 50002500 – 8000
12″DN300500 – 1200—3500 – 90002500 – 80003500 – 12000

Cv Formulas — Quick Reference

Liquid

Cv = Q × √(SG / ΔP)
Q = Flow (GPM)
SG = Specific Gravity
ΔP = Pressure Drop (PSI)

Gas

Cv = (Q/1360) × √(G×T / ΔP×P2)
Q = SCFM, G = SG vs Air
T = Temp (°R), P2 = Outlet (PSIA)
Choked when ΔP/P1 ≥ 0.75

Steam

Cv = W / (2.1 × √(ΔP × P2))
W = lb/h, ΔP & P2 in PSI
Choked: Cv = W / (1.83 × P1)
Superheat correction applied

Frequently Asked Questions

+ What is Valve Cv?

Cv (flow coefficient) is the number of US gallons of water at 60°F that will flow through a valve with a 1 PSI pressure drop when fully open. It is the standard measure of valve capacity used worldwide for sizing control valves, isolation valves, and regulating valves in industrial piping systems.

+ What is the formula for liquid Cv?

The liquid Cv formula is Cv = Q × √(SG / ΔP) where Q is flow rate in GPM, SG is specific gravity (water = 1.0), and ΔP is pressure drop in PSI. This formula applies to incompressible Newtonian fluids.

+ What is choked flow in gas or steam valves?

Choked flow occurs when the pressure drop across the valve reaches a critical ratio. For gas, choked flow begins when ΔP/P1 ≥ 0.75. Beyond this point, increasing the pressure drop does not increase the flow rate. The Cv calculator automatically detects choked conditions and uses the critical flow formula.

+ How do I select the right valve size from Cv?

Always select a valve with a rated Cv at least 20% higher than your calculated Cv to provide a safety margin and allow for minor flow variations. The calculator provides the minimum recommended size. For control valves, a valve sized too large may operate in the low-opening range where control is poor.

KELOR Valves — Krishna Industries, Ahmedabad, Gujarat, India