Cv to Flow Calculator for Construction Systems

Calculator Inputs

Enter your Cv and pressure drop to estimate flow.

Valve Cv

Typical for balancing and control valves.

Pressure drop (ΔP)

Use the drop across the valve only.

ΔP unit

Specific gravity (SG)

Water ≈ 1.0, glycol mixes are higher.

Output flow unit

Fluid temperature (optional)

Shown on exports and reports.

Pipe inside diameter (optional)

Adds velocity checks for noise and erosion.

Project notes (optional)

Included in the PDF and CSV exports.

Calculation is based on the common liquid Cv relationship. Always verify with equipment schedules and manufacturer data.

Example Data Table

Illustrative values for quick comparison.

Cv	ΔP (psi)	SG	Flow (gpm)	Flow (m³/h)	Headloss (ft)
6	4	1.0	12.0000	2.7255	9.2400
12	5	1.0	26.8328	6.0940	11.5500
20	8	1.05	55.0460	12.5038	17.6000

Table values use the same formula as the calculator.

Formula Used

Liquid (incompressible) sizing relationship.

For liquids, the standard relationship is: Q(gpm) = Cv × √(ΔP(psi) / SG).

Rearranged for pressure drop: ΔP(psi) = SG × (Q / Cv)².

Equivalent headloss is estimated by: Head(ft) = 2.31 × ΔP(psi) / SG. Unit conversions are applied for other flow outputs.

How to Use This Calculator

A practical workflow for construction applications.

Find the valve Cv from submittals or a datasheet.
Enter the expected valve pressure drop at design.
Set the fluid specific gravity for your water mixture.
Choose the output unit used in your schedule.
Optionally enter pipe inside diameter to check velocity.
Calculate, then export CSV or PDF for records.

Technical Article

Field-ready guidance for interpreting Cv-to-flow results.

1) Why Cv matters in construction hydronics

Valve Cv links design intent to measurable flow. During balancing and commissioning, Cv helps verify whether a selected valve can deliver required coil, riser, or branch flow at the available differential pressure.

2) Core relationship and unit basis

This calculator uses the standard liquid relationship Q(gpm) = Cv × √(ΔP/SG). Cv is defined at 60°F water for 1 psi drop, so ΔP must be expressed in psi and fluid effects are handled through specific gravity.

3) Typical ranges you will see on site

Small terminal valves often fall in the Cv 0.5–6 range, medium coil valves in 6–20, and larger control or balancing valves in 20–80+. These values vary by trim, stroke, and manufacturer, so always compare against approved submittals.

4) Selecting a practical pressure drop

For stable control, many water systems target a valve drop that is meaningful compared to piping losses. As a working check, 3–10 psi across a control valve at design flow is common, while balancing valves may be set to measurable drops for repeatable readings.

5) Specific gravity data for common fluids

Water is near SG 1.00. Ethylene or propylene glycol mixtures increase SG; for example, a 30% glycol mix can be around SG 1.03–1.05 depending on temperature. Higher SG reduces flow for the same Cv and ΔP, so always enter the correct mixture.

6) Velocity check using optional pipe diameter

When pipe inside diameter is provided, the calculator estimates velocity. In hydronic piping, many teams aim to keep velocity within practical limits to reduce noise and erosion risk. Use this as a screening check alongside your project specifications.

7) Interpreting the headloss output

The reported headloss converts ΔP into equivalent head. This helps align valve losses with pump curves and total dynamic head. It is especially useful when documenting design assumptions, comparing valves, and explaining why a valve authority target is met.

8) Reporting, traceability, and handover

Export the CSV for calculations, schedules, and QA logs. The PDF report is useful for submittal reviews, field checks, and turnover packages. Record Cv source, design ΔP, fluid SG, and any notes so future troubleshooting has clear baseline data.

FAQs

Quick answers for frequent design and field questions.

1) Can I use this for air or steam?

No. The equation here is for incompressible liquids. Gas sizing needs different relationships, pressure ratios, and manufacturer curves to address compressibility, choked flow, and noise limitations.

2) What happens if I increase pressure drop?

Flow rises with the square root of ΔP. Doubling ΔP increases flow by about 41%, assuming Cv and SG remain constant and the valve is operating in its normal control range.

3) How do I choose specific gravity for glycol?

Use the glycol concentration and expected operating temperature, then take SG from the fluid supplier chart. If you only have the mixture percentage, start with a conservative SG and refine during submittal review.

4) Why does the calculator show a ΔP check value?

It back-calculates ΔP from the computed flow and Cv to confirm internal consistency. It should match the input ΔP after unit conversion, aside from rounding.

5) Does pipe size affect the Cv-to-flow calculation?

Not directly. Cv already captures the valve capacity at a given drop. Pipe size is used here only to estimate velocity, which supports practical checks for noise, erosion, and project limits.

6) What is a quick field example?

If Cv is 12, ΔP is 5 psi, and SG is 1.0, the flow is about 26.83 gpm. This matches the example table and can be used to validate readings during balancing.

7) How accurate are the exported CSV and PDF?

Exports capture the displayed inputs, converted ΔP in psi, and computed outputs with rounding. Accuracy depends on correct Cv and ΔP selection, plus the correct specific gravity for your fluid.