Cv to GPM Converter (Water, ISA 75.01)
Per ISA 75.01-2012, the relationship between valve flow coefficient Cv and the resulting water flow is: GPM = Cv × √(ΔP / SG). Cv is defined as the flow in GPM of water (SG = 1.0)...
Formula
Source: ISA 75.01-2012 (Control Valve Sizing Equations); Fisher Control Valve Handbook (5th ed.) | Last reviewed: July 3, 2026
Examples
25.8 cv
= 99.9 GPM (US)
- delta_p = 15
- sg = 1
Cv 25.8, 15 psi ΔP water → 100 GPM (the reference Cv definition)
50 cv
= 158 GPM (US)
- delta_p = 10
- sg = 1
Cv 50, 10 psi ΔP water → 158 GPM
100 cv
= 500 GPM (US)
- delta_p = 25
- sg = 1
Cv 100, 25 psi ΔP water → 500 GPM (typical chiller control)
200 cv
= 1414 GPM (US)
- delta_p = 50
- sg = 1
Cv 200, 50 psi ΔP water → 1414 GPM (large cooling tower)
Quick Reference Table
| Valve Size | Cv Range | Typical GPM at 15 psi ΔP | Application |
|---|---|---|---|
| 1/2" globe | 0.1 - 5 | 0.4 - 19 | Chemical injection, small flow |
| 1" globe | 5 - 30 | 19 - 116 | Small process, instrument air |
| 2" globe | 30 - 120 | 116 - 465 | Process control, cooling water |
| 3" globe | 100 - 300 | 387 - 1162 | Large process, chiller flow |
| 4" globe | 200 - 600 | 774 - 2324 | Cooling tower, condenser |
| 6" globe | 400 - 1500 | 1549 - 5809 | Main distribution |
| 8" globe | 800 - 3000 | 3098 - 11619 | Large industrial |
Where is this used?
In process control, the engineer specifies a desired Cv for a given ΔP and flow requirement, then selects a valve with Cv ≥ required (typically with 20-30% margin).
Common applications: cooling water control valves (Cv 25-200 for 100-1000 GPM service), chemical injection valves (Cv 0.1-5), pump recirculation control valves (Cv 50-500), and tank level control valves.
The Cv-to-GPM formula does NOT apply to compressible (gas/steam) service — use the gas/steam Cv calculators instead.
Real-World Usage Scenarios
Cooling Water Control Valve Sizing
A chemical plant needs to control cooling water flow to a heat exchanger at 250 GPM with a design pressure drop of 12 psi. Required Cv = 250/√12 = 72.2. Selecting a 2-inch globe valve with a maximum Cv of 120 (50% margin): GPM at design ΔP = 120 × √12 = 415 GPM. The actual operating range is 35-250 GPM, well within the valve's 1:10 rangeability (12-1200 GPM). However, the engineer notes that the system pressure drop is 25 psi total (12 across heat exchanger + 8 in piping + 5 in control valve at full flow). The valve authority is β = 5/25 = 0.20 — below the 0.25 threshold. The engineer selects a smaller valve trim (Cv 60 max) to push authority to 0.30.
Common Mistakes to Avoid
Applying Cv-to-GPM to gas or steam service
The GPM formula applies to LIQUIDS (incompressible). For gases, vapors, or steam, the formula includes an expansion factor Y and the compressibility ratio x. Using GPM = Cv × √(ΔP/SG) for a gas will over-predict flow by 5-50% depending on pressure ratio. Use valve-cv-calculator-gas for compressible service.
Forgetting the specific gravity for non-water fluids
For a hydrocarbon (SG = 0.72) at the same Cv and ΔP, the GPM is HIGHER than water because the lower-density fluid flows more easily. GPM = Cv × √(ΔP/SG) = Cv × √(15/0.72) = Cv × 4.56, vs Cv × 3.87 for water. A 15% difference that scales to a 15% over-prediction of cooling capacity if uncorrected.
Industry Standards Referenced
Frequently Asked Questions
What is Cv exactly?
Per ISA 75.01, Cv is the number of US gallons per minute of water (at 60°F) that flows through a valve with a 1 psi pressure drop across it. A valve with Cv = 25 passes 25 GPM of water at 1 psi ΔP. The metric equivalent is Kv (1 Cv = 1.156 Kv, where Kv uses m³/h at 1 bar).
How do I size a valve for a required flow?
Required Cv = Q(GPM) / √(ΔP/SG). For 100 GPM at 15 psi ΔP water: Cv = 100/√15 = 25.8. Select a valve with Cv at least 20-30% higher than required (so 30-35 minimum) to ensure good control range. Verify valve authority β = ΔP_valve / ΔP_system ≥ 0.5.
What is valve authority and why does it matter?
Valve authority β is the ratio of valve pressure drop to total system pressure drop at design flow. β ≥ 0.5 is the rule of thumb (Fisher handbook). Below 0.25, the valve is nearly fully open at design flow, and small stroke movements cause large flow changes — control becomes unstable. To fix: select a smaller valve body (lower max Cv) or add system resistance.
Reviewed for accuracy
Cross-referenced against ISA 75.01-2012 and Fisher handbook worked examples · Last reviewed: July 3, 2026
All calculations are for reference only. Always verify with manufacturer data and a qualified engineer for critical applications. Learn about our editorial process.