The cathedral has a total of twenty one bells in the three towers:
The South West Tower (Oxford Tower) contains the cathedral's main ring of bells, hung for change ringing in the English style. There are fourteen bells – a ring of twelve with two semi-tones, which allow for ringing on ten, eight or six bells while still remaining in tune. All of the bells were cast in 1981 by the Whitechapel Bell Foundry from seven bells of the old peal of twelve with new metal added and rehung in a new frame. The length (draught) of the ropes was increased by lowering the floor of the ringing chamber to the level of the south aisle vault at the same time, also allowing for the new bells to be set lower in the belfry than the old, with the intention of reducing strain on the Medieval structure. The heaviest bell of this ring weighs 34 cwt (1.72 tonnes). The ringers practise on Thursday at 7.15pm.
The North West Tower (Arundel Tower) contains the cathedral's clock chime. The five quarter chimes were taken from the old peal of twelve in the Oxford Tower (where the clock was originally), and hung from beams in the Arundel Tower. The chimes are stuck on the eighth Gregorian tone, which is also used at Merton College, Oxford. The hour is struck on Great Dunstan, the largest bell in Kent 63cwt (3.2 tonnes), which is also swung on Sunday mornings for Matins.
In 1316 Prior Henry of Eastry gave a large bell dedicated to St Thomas, which weighed 71½ cwt (3.63 tonnes). Later, in 1343, Prior Hathbrand gave bells dedicated to Jesus and St Dunstan. At this time the bells in campanile were rehung and their names recorded as "Jesus", "Dunstan", "Mary", "Crundale", "Elphy" (Ælfheah) and "Thomas". In the great earthquake of 1382 the campanile fell, destroying the first three named bells. Following its reconstruction, the other three bells were rehung, together with two others, of whose casting no record remains.
The oldest bell in the cathedral is Bell Harry, which hangs in a cage atop the central tower to which the bell lends its name. This bell was cast by Joseph Hatch in 1635, and is struck at 8am and 9pm every day to announce the opening and closing of the cathedral, and also occasionally for services as a Sanctus bell.
The cathedral also has custody of the bell of HMS Canterbury, a World War I-era light cruiser, hung near the Buffs Chapel in the South West Transept.