How to measure time with your fingernails. I measured one of my fingernails grew 8 millimetres in the space of 58 days. 58 ÷ 8 = 7.25 days So for, approximately, every week that goes by, my nail grows 1 millimetre. A year has 52 weeks my nail grows around 52 millimetres (5.2 centimetres) a year. The exact calculation being: 365.25 ÷ 7.25 = 50.38 (approx.) My fingernail grows around 50.38 (5.038 cm) millimetres a year. Mthoko Mpofana timescale. In the conjectural Zulu measuring system , it's: 50.38 ÷ 7 = 7.19714 A fingernail grows approximately 7.19714 amaqhuzu a year.