A 4–20 mA signal maps linearly onto a process range: 4 mA is the bottom of the range (0%) and 20 mA is the top (100%). Enter a mA value or a process value below and this 4-20mA calculator converts the other one instantly.
Free · No sign-up · Works for pressure, temperature, level and flow · Also handles 0–20 mA, 1–5 V and 0–10 V
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Show reference formula
Signal = Signal_lo + % × (Signal_hi − Signal_lo)
(Signal → PV runs the same equations in reverse.)
| Signal | % of range | 0–10 bar | 0–150 °C | 0–5 m level |
|---|---|---|---|---|
| 4 mA | 0% | 0 bar | 0 °C | 0 m |
| 6 mA | 12.5% | 1.25 bar | 18.75 °C | 0.625 m |
| 8 mA | 25% | 2.5 bar | 37.5 °C | 1.25 m |
| 10 mA | 37.5% | 3.75 bar | 56.25 °C | 1.875 m |
| 12 mA | 50% | 5 bar | 75 °C | 2.5 m |
| 14 mA | 62.5% | 6.25 bar | 93.75 °C | 3.125 m |
| 16 mA | 75% | 7.5 bar | 112.5 °C | 3.75 m |
| 18 mA | 87.5% | 8.75 bar | 131.25 °C | 4.375 m |
| 20 mA | 100% | 10 bar | 150 °C | 5 m |
The formula
How to convert 4–20 mA to a process value
The loop current is proportional to the process variable, so one formula converts in either direction.
mA to process value: PV = LRV + (mA − 4) ÷ 16 × (URV − LRV)
Process value to mA: mA = 4 + (PV − LRV) ÷ (URV − LRV) × 16
LRV and URV are the lower and upper range values the transmitter is configured for, and 16 is the span of the signal (20 − 4). For a 0–20 mA signal, use 0 in place of 4 and 20 in place of 16.
Worked examples
4–20 mA examples
Temperature
A temperature transmitter is ranged 0–200 °C and outputs 10 mA.
(10 − 4) ÷ 16 × 200 = 75 °C
Level
A level transmitter is ranged 0–5 m and outputs 14 mA.
(14 − 4) ÷ 16 × 5 = 3.125 m
Pressure
A pressure transmitter is ranged 0–16 bar and outputs 6 mA.
(6 − 4) ÷ 16 × 16 = 2 bar
Fault levels
What the milliamp value is telling you
0 mA
No current. Usually an open loop, a broken wire or no loop power. A healthy 4–20 mA loop never sits at 0 mA.
3.8 – 20.5 mA
The valid measurement band under NAMUR NE43, which allows a little under-range and over-range.
3.6 mA or less
The NAMUR NE43 downscale fault level. A transmitter that detects a sensor or electronics failure can be set to drive here.
21 mA or more
The NAMUR NE43 upscale fault level. Configure your PLC or DCS to raise an alarm on both fault levels.
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FAQ
4–20 mA questions
What is the difference between 4–20 mA and 0–20 mA?
With 0–20 mA, a reading of 0 mA looks the same as a broken wire or lost power. 4–20 mA reserves the bottom 4 mA as a “live zero”, so a real 0% reading (4 mA) is distinguishable from a fault (0 mA), and a two-wire transmitter can be powered from the loop itself. That is why 4–20 mA is the standard for process transmitters, while 0–20 mA turns up on some drives, recorders and older equipment.
How do I scale a 4–20 mA signal in a PLC?
An analog input card returns raw counts that vary linearly with current. Take the counts at 4 mA and at 20 mA from the card manual (many cards read 4 mA as 0 and 20 mA as 27648, for example Siemens S7), then PV = LRV + (counts − counts at 4 mA) ÷ (counts at 20 mA − counts at 4 mA) × (URV − LRV). Always confirm the counts in the manual for your exact card.
Can I convert 4–20 mA to 1–5 V or 0–10 V?
Yes. A 250 Ω precision resistor across the input turns 4–20 mA into 1–5 V (V = I × R). A resistor alone cannot produce a clean 0–10 V, because it cannot offset and scale the signal, so use a signal converter or isolator for that.
Why does my transmitter read 3.8 mA or 20.5 mA?
Many transmitters are allowed to go slightly past their range before they flag an error. NAMUR NE43 treats 3.8–20.5 mA as valid measurement information, so a value just outside 4–20 mA usually means the process is a little under- or over-range, not a fault. Compare it with the range configured in the transmitter.
How do I check a 4–20 mA loop with a multimeter?
Break the loop, put the meter in series on its mA range, and compare the reading with the value you expect from the calculator above. Many transmitters have a test terminal across a small diode that lets you read the loop current without breaking it. Never connect a meter set to mA across the supply.
How accurate is this 4-20mA calculator?
It uses the standard linear 4–20 mA relationship, so the maths is exact. Your real loop will also carry the transmitter’s own accuracy, the input card’s resolution and any wiring or burden resistor error, so check calibration-critical values against the instrument datasheet.
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