Outs × 4 ≈ flop-to-river %. Outs × 2 ≈ turn-to-river %. Field estimate — remove dirty outs that make you second-best.
Example: 8 outs on flop → ~32% to river. On turn → ~16%. Adjust down for dirty outs.
Dirty outs: flush draw on a paired board may make them a boat when you 'hit.' Count clean outs.