1. How many square metres? (Say 60m2)
2. How wide are the boards? (Say 130mm)
3. What distance between nails? (Say 310mm)
Calculation
Take m2 (eg 60) divide it by board size in metres
(eg 130 mm face = 0.130 metres)
divided it by distance of centres
(eg 310mm = 0.31 metres) number of nails required = 1488.