4-20mA Current Loop Calculator
Convert a 4-20mA, 0-10V, or 1-5V process signal to engineering units and back. Scale sensor readings to PSI, °C, %, or any range — with NAMUR fault flags. Free.
4-20mA scaling quick reference
A 4-20mA transmitter maps its measured range linearly onto the loop current. 4mA is 0% of span, 20mA is 100%, and every point in between is proportional. For a 0-100 PSI sensor:
| Signal (mA) | % of span | 1-5V equivalent | 0-100 PSI reads |
|---|---|---|---|
| 4 mA | 0% | 1.0 V | 0 PSI |
| 8 mA | 25% | 2.0 V | 25 PSI |
| 12 mA | 50% | 3.0 V | 50 PSI |
| 16 mA | 75% | 4.0 V | 75 PSI |
| 20 mA | 100% | 5.0 V | 100 PSI |
Why 4mA instead of 0?
The 4mA "live zero" is what lets you tell a real 0% reading apart from a dead loop. A healthy sensor at the bottom of its range still draws 4mA; a broken wire, failed transmitter, or reversed polarity drops the current toward 0mA. Most PLCs and transmitters follow the NAMUR NE43 convention: below 3.6mA or above 21mA is flagged as a sensor fault rather than a valid process value — which is why this calculator warns you when a reading crosses those thresholds.
Getting an under-range or erratic reading on a loop? The 4-20mA current loop wiring & troubleshooting guide walks through the usual causes — loop power, burden resistance, grounding, and how to check a transmitter with a meter.