Instrumentation
4–20 mA Transmitter Calculator
Convert between engineering value, percent of span, and signal for 4–20mA, 0–20mA, 1–5V, or 0–10V transmitters.
Range & signal
Signal → PV
PV → Signal
Result
Enter values and calculate.
About This Calculation
A 4-20mA transmitter compresses a physical measurement's entire calibrated range into a standard current signal, with 4mA representing the low end (0%) and 20mA the high end (100%) — the choice of 4mA rather than 0mA as the zero point is deliberate: it lets a broken wire or dead transmitter be distinguished from a genuine zero reading, since a real zero reads 4mA while a fault reads 0mA. This tool converts between the engineering value, the percentage of range, and the corresponding mA signal for any transmitter's calibrated span.
Frequently Asked Questions
Why 4-20mA specifically, instead of 0-20mA or another range?
The 4mA live zero is the key design choice — it lets the receiving instrument (PLC, DCS, indicator) distinguish a genuine zero reading (4mA) from a broken wire, dead transmitter, or disconnected loop (0mA), which a 0-20mA scheme cannot do at all.
How is the milliamp value related to percentage of range?
Linearly: 4mA = 0% of range, 20mA = 100% of range, with every point in between scaling directly — 12mA is always 50% of range regardless of what the range actually represents in engineering units, which is exactly what makes 4-20mA a universal signal standard across different measurement types.
Does a transmitter’s calibrated range have to match its physical measurement limits?
No, and usually it shouldn’t — a transmitter is calibrated to the RANGE the specific application needs (e.g. 0-10 bar) even if the physical sensor could measure a wider range, since using the full 4-20mA span across only the range actually needed maximizes resolution and accuracy for that application.