Enter project inputs
Use the form below to estimate a preliminary regulator size for construction gas service work, plant utility distribution, or temporary fuel systems.
Example data table
| Scenario | Gas | Connected Flow (m³/h) | Inlet (kPa g) | Outlet (kPa g) | Required Cv | Sample Size |
|---|---|---|---|---|---|---|
| Site kitchen manifold | Natural gas | 180 | 50 | 18 | 6.1 | 3/4 in |
| Temporary boiler yard | Natural gas | 420 | 70 | 21 | 12.9 | 1 in |
| Propane vaporizer feed | Propane vapor | 310 | 120 | 35 | 16.8 | 1-1/4 in |
| Plant expansion reserve | Custom SG 0.72 | 650 | 90 | 28 | 24.7 | 1-1/2 in |
Formula used
- Design flow: Connected Flow × Diversity Factor × (1 + Growth Allowance) × (1 + Safety Factor).
- Absolute pressure: Gauge Pressure + 101.325 kPa.
- Actual inlet flow: Standard Flow × (Pstd / Pin,abs) × (Tin / Tstd) × Z.
- Inlet gas density: ρair,std × SG × (Pin,abs / Pstd) × (Tstd / Tin) ÷ Z.
- Equivalent flow area: Qactual ÷ (3600 × Cd × Target Velocity).
- Equivalent diameter: √(4A / π).
- Approximate Cv screening: Qscfh ÷ [1360 × √((P1² − P2²) ÷ (SG × T × Z))].
These equations provide a practical preliminary estimate. Final regulator sizing should always be checked against manufacturer flow curves, droop limits, noise limits, shutoff class, and code requirements.
How to use this calculator
- Choose the gas type, or select custom and enter a specific gravity.
- Enter the connected standard flow rate expected on the project.
- Apply a diversity factor if all loads will not operate together.
- Add future growth and safety margins for conservative selection.
- Enter inlet and required outlet pressure in kPa gauge.
- Set temperature, Z factor, discharge coefficient, and target velocity.
- Press the calculation button and review the size, Cv, velocity, and warnings.
- Download CSV for schedules or PDF for design review records.
Frequently asked questions
1. What does this calculator estimate?
It estimates a preliminary gas regulator size using standard flow, pressure conditions, gas properties, design margins, required Cv, and a sample body-size catalog comparison.
2. Why do I enter gauge pressure instead of absolute pressure?
Construction drawings usually show gauge pressure. The calculator automatically converts those values to absolute pressure before using gas-capacity equations.
3. When should I use a diversity factor below 1.00?
Use a lower factor when connected appliances will not all operate together. This reduces design flow and may prevent oversizing.
4. Is the selected size ready for procurement?
Not by itself. Confirm the final model with manufacturer capacity charts, lockup behavior, materials, relief requirements, and project code obligations.
5. What does capacity utilization tell me?
It shows how hard the selected sample regulator works relative to its catalog Cv. Lower utilization usually leaves more operating margin.
6. Why is velocity included in the check?
High internal gas velocity can increase noise, erosion risk, and control instability. The velocity check helps screen against aggressive port loading.
7. Can I use this for propane vapor service?
Yes. Select propane vapor or enter a custom specific gravity if your supplier provides a more accurate value.
8. Why do warning notes appear for low pressure ratios?
Large pressure cuts can move the regulator toward critical-flow or noisier operating regions. That condition deserves a manufacturer review.