One of aviation's Rules of Thumb...
an approximate best approach speed is found halfway between the top and
bottom of the white arc.

Cockpit Colin wrote:
Something that's always worked for me ...
Take Vso (bottom of white arc) - reduce it by 5% for every 10% under MAUW
then multiply it by ...
1.3 for over the fence speed
1.4 for Base
1.5 for downwind
Works for all aircraft I've flown (although I add a bit in C172 - Vso
(adjusted) can be as low as 28 knots - so at 28 * 1.3 (approx 37) it still
hasn't stalled, but controls are getting pretty mushy (any people who bring
them over the fence at 65 to 70 wonder why they float!)