Instrumentation
4–20 mA Scaling Calculator
In industrial instrumentation, a 4–20 mA current loop represents a process variable across its calibrated range. 4 mA corresponds to the lower range value (LRV) and 20 mA corresponds to the upper range value (URV). This calculator converts between mA signal and scaled process values using the standard linear relationship.
TypeInteractive calculator — separate from unit conversions
Calculator
mA
Results
Percent of span50%
Process value50 kPa
Formulas
Percent of span
% span = (mA − 4) / 16 × 100
Process value from mA
PV = LRV + ((mA − 4) / 16) × (URV − LRV)
mA from process value
mA = 4 + 16 × ((PV − LRV) / (URV − LRV))
Diagram
Worked example
A pressure transmitter is ranged 0–100 kPa (LRV = 0, URV = 100). The signal reads 12 mA. What is the process value?
- 01% span = (12 − 4) / 16 × 100 = 50%
- 02PV = 0 + ((12 − 4) / 16) × (100 − 0)
- 03PV = 0 + 0.5 × 100 = 50 kPa
Result
At 12 mA, the process value is 50 kPa (50% of span).
FAQ
Does this calculator handle square-root extraction for DP flow?
No. Square-root extraction is a separate function applied to the scaled output and is not implemented in this calculator. The output is always linear.
Can I use this for 0–20 mA signals?
This calculator is designed for the standard 4–20 mA range. For 0–20 mA signals, the formulas would differ (replace 4 with 0 and 16 with 20).
What happens if my mA reading is outside 4–20?
The calculator will still produce a result, but the value will be flagged as out-of-range. Readings below 4 mA or above 20 mA may indicate a wiring fault or sensor failure.
What is the engineering unit label for?
It is a free-text label so you can note what the process variable represents (e.g., "kPa", "degC", "L/s"). It does not affect the calculation.