DrawOuts0–60% scaleNext cardBy the river
Pocket pair → set24%8%
Gutshot straight48%16%
Two overcards612%24%
Open-ended straight816%32%
Flush draw918%36%
Flush + gutshot1224%48%
Flush + open-ended1530%≈54%
by the turnby the river
Rule of 2 and 4: outs × 2 for one card to come, outs × 4 for two. It overstates monster draws slightly — 15 outs is ≈ 54% in reality, still an easy yes.