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4–20 mA Signal Scaling Calculator

Convert current and engineering values in either direction across a linear 4–20 mA span.

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Your inputs

01 / Enter

These are editable examples, not recommended rates. Enter your own numbers.

Calculator inputs

Only the selected source is used; both source fields retain their editable values.

Current source in mA. Values outside 4–20 are extrapolated with a warning.

May be above the 20 mA endpoint for a descending range.

Must differ from the 4 mA endpoint.

All measurements use this same unit. Changing the label does not convert input values.

Your result

02 / Understand

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Show the math

Calculations retain numerical precision. Displayed quantities are rounded to significant digits, not to cents.

What this means

The fraction of span links current and engineering units. The 4 mA endpoint represents 0% and the 20 mA endpoint represents 100%, even when the engineering range descends.

Worked example

For 0–200 psi, 12 mA is 50% of span and 100 psi. Reversing 100 psi gives 12 mA. A descending 100–0 range gives 50 units at 12 mA; 24 mA extrapolates to −25 units (125%).

How the math works

Fraction p = (current − 4)/16. Engineering value = lower + p×(upper−lower). Reverse: p = (engineering−lower)/(upper−lower); current = 4+16p. Percentage of span = 100p.

About this estimate

Linear 4–20 mA scaling only. Endpoints cannot be identical. Out-of-range results remain visible and are not silently clamped. This is not square-root extraction, an alarm-state decoder or a claim about hardware behavior.

Reference conventions

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Formula v1.0.0 · Reviewed · Tool ID: signal-scaling-4-20ma