The required equity when the bet is ⅓, ½, ¾, pot, or 2x pot.
Memorize the sequence. Facing a bet of 5 into a pot of 10 (½), you need 25%. Win once in 4 and you break even. Exact values: ⅓ is 20.0%, ½ is 25.0%, ¾ is 30.0%, pot is 33.3%, 2x is 40.0%. A ⅔-pot bet needs 28.6%.