4–20 mA calculator

Convert loop current to a process value, or a process value to the current your transmitter should send.

Range low (at 4 mA)

Range high (at 20 mA)

Units

Loop current (mA)

Process value

Percent of span
Span

Percent	Current	Value

How it works

A 4–20 mA loop maps the measuring range linearly onto 16 mA of current. 4 mA is the bottom of the range, not zero current, so a broken wire (0 mA) is distinguishable from a real low reading.

value = LRV + (mA − 4) ÷ 16 × (URV − LRV) mA = 4 + 16 × (value − LRV) ÷ (URV − LRV)

NAMUR NE43 signal ranges

Many transmitters follow the NAMUR NE43 recommendation: valid measurements run from 3.8 to 20.5 mA, and currents at or below 3.6 mA or at or above 21 mA signal a device fault. Check your device's manual, as not every transmitter follows it.