These vary from commission to commission but the British Boxing Board of Control regulations are fairly typical, they state :-
All contests shall be decided in a four-rope ring not less than 16 foot nor more than 20 feet square and with the ropes joined together in the centre of each side. The bottom rope should not be more than 14 inches from the floor of the ring to the top of the bottom rope and ropes above this should be no more than 12 inches from centre to centre. The tension of the bottom rope should be considerably less than the tension of the top three. There must be at least an 18 inch margin of ring floor outside the ropes and the floor must be covered with canvas over a safety mat approved by the Board. Each corner should be padded from the top of the bottom rope with one whole length of padding not less than two inches thick and six inches wide.