What bridge compensation is
Pressing a string down to a fret stretches it slightly, which raises its pitch a little sharp. To cancel that, the saddle is moved back so the string is a touch longer than the nominal scale length. The total nut-to-saddle distance is the scale length plus the compensation for that string.
What affects it
Compensation depends on the string gauge and construction, the tension, and the action height. As a rule, thick wound strings need noticeably more compensation than thin plain strings, which is why saddles on electric and acoustic guitars are slanted or stepped.
Examples from this calculator on an electric guitar with a 25.5" scale: a .010 plain steel string tuned to E4 comes out at about 0.039" (1.0 mm), and a .046 nickel-wound string tuned to E2 at about 0.238" (6.0 mm).
How the estimates are built
Compensation is estimated with empirical models fitted separately for each instrument family (electric guitar, acoustic guitar, bass, nylon-string bass, ukulele, baritone ukulele and mandolin), calibrated against published string data and an independent reference calculator. Errors are checked in thousandths of an inch. The calculator warns you when a string falls outside the range its data covers.
Treat the numbers as a strong starting point. Final intonation is always set with a tuner: compare the 12th-fret harmonic with the fretted 12th fret, and adjust the saddle until they agree.
Supported instruments
6, 7, 8 and 9-string guitar, 12-string guitar, classical guitar, 4, 5 and 6-string bass, nylon-string bass, soprano, concert, tenor, low-G tenor and baritone ukulele, and mandolin. Multi-course instruments such as the 12-string and mandolin are handled per course.
Frequently asked questions
How much compensation does a guitar need?
It varies by string. On a typical electric guitar the thinnest string needs roughly a millimetre or so and the thickest wound string several millimetres. Use the calculator for your gauges and scale length instead of a rule of thumb.
Do wound strings need more compensation than plain strings?
Generally yes. Thicker, stiffer wound strings need more than thin plain strings, which is why the low strings sit further back on a compensated saddle.
Is the result exact?
No. It is an estimate fitted to real data. Action height, string brand and setup all shift the ideal value, so confirm with a tuner and adjust the saddle.