Converting points of rain to mm is easy once you know one number: one point is 0.254 millimetres. Plenty of older farmers still talk in points, and many family rain books were kept that way before Australia switched to millimetres in the 1970s.
What are points of rain?
A point is one hundredth of an inch. So 100 points is one inch of rain, which is 25.4 mm.
Points of rain to mm: the quick rule
Divide the points by four and you're close enough for a yarn over the fence. 50 points is roughly 12 mm. For exact figures, multiply by 0.254.
- 10 points = 2.5 mm
- 25 points = 6.4 mm
- 50 points = 12.7 mm
- 100 points (1 inch) = 25.4 mm
- 200 points (2 inches) = 50.8 mm
Keeping old and new records together
If your rainfall records go back to points and inches, you don't have to convert them by hand. In the GaugeMate rain gauge app you can switch between millimetres, points and inches at any time, and every total, chart and report follows along. Grandad's rain book and this morning's reading finally line up.