Math Shortcut - feet per second

Feet Per Second = MPH * 1.5
MPH = Feet Per Second * 2/3

• 60 mph is about 90 feet per second (88 exactly), so just multiply by 1.5. Or, just add half to itself (60 + 30 = 90).
• Going 100 mph? That’s 150 fps.
• Going 10 fps? That’s about 7 mph (10 * 2/3 is 6.666). Or, just take away 1/3 (10 – 3 = 7).

Source: Mental Math Shortcuts