Rate calculation

The rate of a clock is determined by two things – the length of the pendulum and the total gear ratio of the time train of the clock. The length of the pendulum determines its natural oscillation rate, and it requires a fairly significant force to overcome its natural rate, which makes them ideal for regulating clocks. The gear train determines how many ticks are required to move the clock hands a certain distance.  While length of the pendulum and gear train are related, they are separate factors. The pendulum’s rate is determined by the laws of physics, while the gear train translates that into the human construct of the minute hand going around once per hour. 

Knowing how to regulate your clock requires either empirical testing over a period of time – comparing your clock to an accurate time source and making corrections, or using a timing device, which requires knowing the target beat rate for the clock.

If you have access to the movement and a careful eye, you can count the teeth in the time train and calculate the correct beat rate for your clock. This page includes instructions and an online calculator if you wish to try this method.

The table below is a list of rates of some clocks expressed in beats per hour (BPH) and beats per minute (BPM). This is far from an exhaustive list as there are a large number of different BPH combinations used over the years. Others have published much longer listsof clock BPH rates.

It is theoretically possible to work the other direction – to start with the length of the pendulum and calculate the BPH rate it would need to swing at to keep time, however in practice this is difficult, as the critical dimension is from the top of the suspension spring to the center of mass of the pendulum. Measuring the center of mass of a pendulum is difficult as it depends on the type and design of the pendulum. For lyre pendulums, the center of mass is above the center of the bob. For stick pendulums, the center of mass is usually slightly below the center of mass.

This is a work in progress and the list will grow over time. Please Contact Us if you have any beat rates to add to the list.

Clock Beat Rates

Clock ManufacturerClock ModelBeats Per Hour (BPH)Beats Per Minute (BPM)Tick Time (Seconds)Comments
AnsoniaCabinet Antique12500208.330.288
AnsoniaPrompt4440740.811
AnsoniaSymbol Crystal Regulator9068.6151.140.397
E HowardNo 70 Regulator5084.784.7450.708
EN WelchPatti No 2 (Baby Patti)10495.6174.9270.343
EN WelchPatti V.P.7523.27125.3870.478
GilbertNo 8 Regulator3600601
GilbertNo 16 Regulator3600601
GilbertNo 20 Regulator3600601
IngramKitchen Clock8489.8141.500.424
IthacaNo 2 Bank405067.50.889
Killam & Co Banjo470478.40.765
Lockwood & Almquist90-Day4800800.75
Seth ThomasAdamantine9777.9162.970.368
Seth ThomasElipse8372139.530.43
Seth ThomasNo 1 Regulator4800800.75
Seth ThomasNo 2 Regulator4800800.75
Seth ThomasOffice Calendar No 25760960.625This is a beat rate of the Office Calendar No 2 reported by others
Seth ThomasOffice Calendar No 25880980.612This is the beat rate of my Office No 2. Apparently a second movement was also used with a slightly different beat rate.
Seth ThomasOffice Calendar No 68372139.530.43
Seth ThomasSelf-winding No 172001200.5
Seth ThomasShips Clock180003000.2
Seth ThomasSummit9100151.670.395
VariousEnglish Dial9050150.830.398
VariousGrandfather/Tallcase clocks3600601
WaterburyRegulator No 34800800.75
WillardBanjo clock470278.40.765

 

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