Proportional band
The error, as a percentage of range, that drives the controller output across its full span. PB% = 100 / gain; raising the band weakens proportional action.
What it means
Proportional band is how much error it takes to move the output from one end of its range to the other. A band of 100% means the error would have to span the whole measurement range to drive the output from 0% to 100%. A band of 50% means half that error does it, so the same mistake produces twice the correction.
The formula is a reciprocal: proportional band as a percentage is one hundred divided by the controller gain, and gain is one hundred divided by the band. Because they are inverses, raising the band is weakening proportional action — the opposite of raising gain.
Honeywell, Yokogawa and Foxboro faceplates show the proportional term as a band. A gain-based system (DeltaV, PCS 7, Rockwell) shows the same quantity from the other end. Convert before you copy a number across.
Also called
On a plant you will hear this called PB, P-band, throttling range. They mean the same thing.
Related
Glossary
Where this comes up
Last reviewed 2026-09-18.