Facts and figures: Big Ben and Elizabeth Tower

The Elizabeth Tower  

Imagine 21 London buses sitting on top of each other. That’s the height of the Elizabeth Tower.  

11 floors. 96 metres.  

It’s a long climb to the top. 334 steps to the Belfry where Big Ben, the Great Bell, hangs. 

Climb another 55 steps and you reach the Ayrton Light, the lantern that shines when the Houses of Parliament are sitting.

Elizabeth Tower is made from: 

• 850 cubic metres of stone 
• 2,600 cubic metres of brick 
• Anston stone from Yorkshire and Clipsham stone from Rutland 
• Caen limestone, imported from France

The Great Clock 

There are 4 clock dials.

Each dial is made of 324 pot opal glass pieces in a cast iron frame. 

The hour figures are 60 centimetres in length. The dials are 7m in diameter.  

The minute hands are made of copper sheet. Each hand weighs 100 kilograms and they are 4.2m long. They travel the equivalent of 190 kilometres a year. That’s the distance from London to Weymouth.

Hour hands are made of gun metal and three times heavier at 300kg. They are 2.7m in length.

The clock mechanism  

The mechanism keeps the Great Clock ticking and Big Ben striking.   

Each pendulum ‘beat’ lasts for 2 seconds.  

It’s adjusted using pre-decimal pennies, which in turn regulate the clock mechanism. Adding one penny causes the clock to gain two-fifths of a second in 24 hours.  

Outside pressure like the wind on the clock hands can affect the clock's accuracy. Edmund Beckett Denison designed the 'Double Three-legged Gravity Escapement' to solve this. It compensates for the effects of outside pressure on the mechanism and is crucial in helping the clock keep accurate time. 

The mechanism:  

• weighs 5 tonnes 
• is made of cast iron 
• is 4.7m long and 1.4m wide 

The pendulum: 

• is 4.4m long 
• weighs 310kg 

The bob weighs 203kg and is made of concentric tubes of steel and zinc. A bob is a weight hanging from a cable that swings from side to side. 

The Bells – Big Ben and the quarter bells 

Big Ben is not the only bell in the clocktower. The bells are fixed and struck by hammers from outside, rather than swinging and being struck from inside by clappers.   

There are four other bells in the Belfry. Their notes all combine to form the famous tune: 

• ‘E’ is Big Ben’s musical note, as is the third quarter bell 
• ‘G’ is the first quarter bell’s musical note 
• ‘F#’ is the note of the second quarter bell 
• ‘B’ is the fourth bell’s note. 

Which is the heaviest? 

• Big Ben weighs 13.7 tonnes, the hammer is 200kg 
• The first quarter bell weighs 1.1 tonnes  
• The second quarter bell weighs 1.3 tonnes 
• The third quarter bell weighs 1.7 tonnes 
• The fourth quarter bell weighs 4 tonnes 

Great Clock stoppages 

• 6 weeks in 2007, the longest stoppage of the hour strike since 1990 
• 6 months in 1956 
• 2 months in 1934 
• 2 days in 2005, so that the brake shaft could be inspected