Proportional band
What is proportional band: the error, as a percent of range, that drives the output across its span. PB% = 100 / gain; raising the band weakens proportional action — the opposite of raising gain.
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.
Questions that come up
What is proportional band?
The error, as a percentage of measurement range, that drives the controller output from 0% to 100%. A band of 100% means the error would have to span the whole range to do it. A band of 50% means half that error does it, so the same mistake produces twice the correction.
What is the proportional band formula?
PB% = 100 / gain, and gain = 100 / PB%. They are reciprocals, so raising the band weakens proportional action — the opposite of raising gain. Convert before you copy a number between a band-based faceplate and a gain-based one.
Related
Glossary
Where this comes up
Written by PIDSnap control engineering. Published 2026-08-01, last reviewed 2026-10-22.