4-20 mA Scaling Calculator
Scale a 4-20 mA loop signal to engineering units.
Runs in your browser. Nothing is uploaded — your input is processed on this device and discarded when you close the tab.
4-20 mA Scaling Calculator
How to use this tool
- Enter the loop current (or engineering value for reverse mode) and the engineering range it maps to.
- Press Generate. The tool scales linearly between 4 mA at the minimum and 20 mA at the maximum.
- Use Load sample for 12 mA over 0 to 100, or Clear to start again.
Worked example
For 12 mA over an engineering range of 0 to 100, the value is 0 + (12 - 4) / (20 - 4) x (100 - 0) = 50. In reverse, an engineering value of 50 over the same range gives 4 + (50 - 0) / (100 - 0) x 16 = 12 mA.
What this tool does not do / Limits
This assumes a perfectly linear 4-20 mA loop with 4 mA at the range minimum and 20 mA at the maximum. Real loops have calibration error, noise and fault currents below 4 mA or above 20 mA, which this tool does not model.
Frequently asked questions
Why does 4 mA mean the minimum, not zero current?
A live zero lets the system tell a real minimum reading apart from a broken wire (0 mA). That fault detection is the main reason the 4-20 mA standard exists.
What happens outside 4-20 mA?
The formula still extrapolates, but a real transmitter reading below about 3.8 mA or above about 20.5 mA usually signals a fault, not a real value — check the instrument before trusting it.
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