Flow Meter K-Factor Calculator
By Santaji GadepatilinUpdated October 27, 2026
Pulse-output flow meters such as turbines, vortex meters and gear meters send a fixed number of pulses per unit volume — the K-factor. It converts pulse frequency into flow rate and pulse count into totals, as explained in these flow meter K-factor calculations.
Pulse frequency vs Flow rate (L/min) — other inputs held at your current values.
How to use the flow meter K-factor calculator
Enter the meter’s K-factor (pulses per litre) and either the flow rate or the measured pulse frequency. The other is calculated. Use it to set up a PLC counter, check a meter on the bench, or choose a frequency input range.
For more background, read Turndown Ratio in Flow Meters.
Flow meter K-factor formula
f (Hz) = K (pulses/L) × Q (L/s) Q = f ÷ K
Worked example
A small turbine meter with K = 450 pulses/L at 6 L/min:
- Q = 6 ÷ 60 = 0.1 L/s
- f = 450 × 0.1 = 45 Hz
At the maximum flow of 20 L/min the output reaches 150 Hz — check the PLC input can count that fast.
Totalising
Volume = pulse count ÷ K-factor. 9,000 pulses ÷ 450 = 20 litres.
K-factor examples
| Meter type | Typical K-factor |
|---|---|
| Small paddle-wheel sensor (DN15) | 300–500 pulses/L |
| Turbine meter, DN25 | 50–150 pulses/L |
| Turbine meter, DN100 | 1–5 pulses/L |
| Positive displacement meter | 1–100 pulses/L |
| Mag meter pulse output | Configurable, e.g. 1 pulse per 10 L |
Always use the calibrated K-factor printed on the meter certificate.
Units conversions
| From | To | Multiply by |
|---|---|---|
| pulses/L | pulses/US gal | 3.785 |
| pulses/L | pulses/m³ | 1,000 |
| pulses/US gal | pulses/L | 0.2642 |
Linearity and the K-factor curve
A turbine meter’s K-factor is not perfectly constant; it varies with flow rate and viscosity. Calibration certificates often give K at several flow points. Many flow computers apply a linearisation table to correct for this.
Choosing the pulse output
Make sure the maximum pulse frequency is within the counter input’s limit, and the minimum gives enough resolution:
- At maximum flow, frequency should be below the input’s maximum (for example 10 kHz).
- At minimum flow, at least a few pulses per second gives a stable rate display.
Tips
- Use the K-factor from the calibration certificate, not the nominal catalogue value.
- K-factors drift slightly with viscosity and at very low flow. Many meters list a linear range where the K-factor holds within ±0.5%.
- For long cable runs, use shielded cable and check the pulse output type (NPN, PNP, Namur or reed).
Frequently asked questions
What is a K-factor?
The number of pulses a meter sends for each unit of volume, such as 450 pulses per litre. It comes from the meter's calibration certificate.
How do I convert pulses per gallon to pulses per litre?
Divide pulses per US gallon by 3.785. A K-factor of 1,700 pulses/gal is about 449 pulses/L.
How do I count total volume?
Divide the total pulse count by the K-factor. 9,000 pulses at 450 pulses/L is 20 litres.
How do I find the K-factor of a flow meter?
Count the pulses while passing a known volume, then divide pulses by volume. Repeat at several flows for accuracy.
How do I convert pulses to total volume?
Total volume = total pulses ÷ K-factor.