Tool

Beat rate converter

Spec sheets give a movement's frequency as vph, bph, A/h or Hz. Enter any of them to convert, see how many steps the seconds hand takes each second, and find catalogue calibers that run at that rate.

Unit

vph, bph and A/h (alternations per hour) are the same thing.

Result

Vibrations / hour
21,600 vph
Frequency
3 Hz
Beats / second
6

Common in affordable and older automatics

A higher rate makes the seconds hand sweep in smaller steps and is often said to shrug off knocks better, but it also wears parts and uses power faster.

Calibers at 21,600 vph

Matched on sourced frequency only.

How the numbers are worked out

  1. A beat is one swing of the balance wheel, one tick or one tock. vph counts beats per hour.
  2. Beats per second = vph ÷ 3,600. That is also the number of steps the seconds hand makes each second.
  3. One full oscillation is two beats, so Hz = beats per second ÷ 2, or vph ÷ 7,200.

Common beat rates

vphHzBeats/sUsually described as
18,000 2.5 5 Slow beat, common in vintage watches
19,800 2.75 5.5 Slow beat
21,600 3 6 Common in affordable and older automatics
25,200 3.5 7 Mid-beat
28,800 4 8 The usual rate for modern mechanical watches
36,000 5 10 Hi-beat

See also: all calibers · movement types