4.000 mA
- Expected
- 0.000 m
- Difference
- —
m
Water/Wastewater Process Tools
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4–20 mA Level Calculator
Calculate expected level readings, check instrument linearity and determine the current required to simulate a level setpoint.
Configured level span
Enter the instrument range once. Every calculation below uses this span.
Required. Decimal values are supported.
m
Calculations assume 4.000 mA = 0.000 m and 20.000 mA = the configured level span.
Setpoint Simulation
Find the signal current corresponding to a specified level within the configured span.
m
Current to simulate setpoint
14.061 mA
62.88% of configured span
(16 ÷ 2.500 × 1.572) + 4 = 14.061 mA
Five-point linearity check
Compare observed readings with the theoretical linear signal values.
| Applied mA | Expected level | Observed level | Difference |
|---|---|---|---|
| 4.000 mA | 0.000 m | m | — |
| 8.000 mA | 0.625 m | m | — |
| 12.000 mA | 1.250 m | m | — |
| 16.000 mA | 1.875 m | m | — |
| 20.000 mA | 2.500 m | m | — |
8.000 mA
- Expected
- 0.625 m
- Difference
- —
m
12.000 mA
- Expected
- 1.250 m
- Difference
- —
m
16.000 mA
- Expected
- 1.875 m
- Difference
- —
m
20.000 mA
- Expected
- 2.500 m
- Difference
- —
m
Custom Signal Conversion
Convert a value in either direction using the configured span.
mA → Level
mA
Expected level 1.250 m
Level → mA
m
Expected current 10.400 mA
Linear level and current conversion
A standard linear 4–20 mA signal maps 4 mA to zero level and 20 mA to the configured measurement span. Enter the span once, then use the five-point check, setpoint simulation and custom converters with the same configuration.
Level = ((mA - 4) / 16) × Span. Current from level uses mA = ((16 / Span) × Level) + 4.
Five-point instrument checks
The five standard points of 4, 8, 12, 16 and 20 mA provide a quick theoretical reference across a linear range. Add observed readings to see only the numerical difference from the expected level.
This calculator deliberately does not define a calibration tolerance or pass/fail result. Apply only your organisation’s approved procedures and the instrument manufacturer’s instructions.
Setpoint support in the field
Enter a level setpoint to find its percentage of the configured span and the corresponding current. The result can support planning and verification work, but applying a signal does not by itself prove alarm logic or any wider control-system response.
FAQs
Questions about the 4–20 ma level calculator
What does 4–20 mA represent?
For this linear calculator, 4 mA represents zero level and 20 mA represents the configured level span.
Does the calculator decide whether an instrument passes?
No. It reports numerical differences only. Tolerances and acceptance criteria must come from approved procedures or the manufacturer.
Can I use a different level span?
Yes. Enter any positive, reasonable span in metres and all sections update from that same value.
Is entered process information uploaded?
No. The calculations run locally in the browser and do not use an external calculation API.