A foot is 30.48 centimetres exactly
The international foot was fixed at 0.3048 metres in 1959, so a foot is 30.48 cm and a centimetre is 0.032808… feet. For heights, enter decimal feet: 5 ft 9 in is 5.75 ft (9 ÷ 12 = 0.75), which converts to 175.26 cm. The height converter takes feet and inches as two separate boxes if you prefer.
centimetres = feet × 30.48 | feet = centimetres ÷ 30.48
Rough conversion in your head
Multiply feet by 30 and add a little: 6 ft → 180 + 3 = 183 cm, against a true 182.9. Going the other way, divide centimetres by 30 and trim slightly: 180 cm → 6 − a touch, so about 5 ft 11 in (true 5.906 ft). The calculator's inch row turns the decimal remainder back into inches for you.