How mA relates to percentage
A 4–20 mA signal carries its information in the 16 mA between the live zero (4 mA) and full scale (20 mA). Percentage of span is simply how far the current has travelled along that 16 mA window:
and in the other direction:
Percentage is the range-independent language of the control room: a technician can say "the signal reads 50%" without knowing whether the transmitter measures pressure, level or temperature, and everyone understands the loop is at mid-scale.
Memory tricks every technician uses
- Every 4 mA = 25%: 4 → 0%, 8 → 25%, 12 → 50%, 16 → 75%, 20 → 100%.
- Every 1 mA = 6.25%, so 13 mA is 50% + 6.25% = 56.25%.
- Every 0.16 mA = 1% — handy when checking calibration tolerances.
Worked example
Your multimeter reads 17.2 mA in series with the loop. What percentage is the signal?
- 17.2 − 4 = 13.2 mA above live zero
- 13.2 ÷ 16 = 0.825
- 0.825 × 100 = 82.5%
Quick reference table
| mA | % | mA | % |
|---|---|---|---|
| 4 | 0 | 13 | 56.25 |
| 5 | 6.25 | 14 | 62.5 |
| 6 | 12.5 | 15 | 68.75 |
| 7 | 18.75 | 16 | 75 |
| 8 | 25 | 17 | 81.25 |
| 9 | 31.25 | 18 | 87.5 |
| 10 | 37.5 | 19 | 93.75 |
| 11 | 43.75 | 20 | 100 |
| 12 | 50 |
Need the actual process value instead of a percentage? Use the 4–20 mA to PV calculator, which applies your LRV and URV. And remember: on a DP flow signal without square root extraction, 50% current is not 50% flow — see the square root extraction calculator.
Frequently asked questions
How do I convert mA to percentage quickly in my head?
Remember that every 4 mA above the live zero equals 25%: 4 mA = 0%, 8 mA = 25%, 12 mA = 50%, 16 mA = 75%, 20 mA = 100%. Each 1 mA is 6.25%.
What percentage is 10 mA on a 4-20 mA signal?
10 mA is 37.5%. Calculation: (10 − 4) ÷ 16 × 100 = 37.5%.
Can the percentage be negative or above 100%?
Yes — currents below 4 mA or above 20 mA produce percentages outside 0-100%, which indicates the process is beyond the calibrated range or the transmitter is signalling saturation or failure.
Provided for reference and education. Verify independently before use in safety-critical work. See our disclaimer.