formula for calculating equity for hands more than 8 outs on the turn

[dfan]

And you can make it even easier, since that formula simplifies to:

Let Y = # of outs
Then
4Y - (Y - 8) =
= 4Y - Y + 8
= 3Y + 8

So 15 outs = (3 * 15) + 8 = 53%
9 outs = (3 * 9) + 8 = 35%

Quite accurate for 9 outs through 20 outs.
For 1 to 8 outs just use 4*Y.