501 darts rules: double out, bust and how a leg ends
Short answer: each player starts on 501. Every turn you throw three darts and subtract their total. The first player to reach exactly zero wins the leg, and the last dart must hit a double (the inner bull counts as a double). If a turn would take you below zero, to exactly one, or to zero without a double, it is a bust and your score goes back to where it was before that turn.
1. Starting score and turns
All players start on 501 (301 is common for shorter games). Players take turns of three darts. The score of the three darts is subtracted from what you have left.
2. Scoring a dart
The outer narrow ring is the double (twice the number), the inner narrow ring is the treble (three times). The outer bull is 25 and the inner bull is 50. The highest three-dart score is 180 (three treble 20s).
3. Double out
To win, the last dart must land in a double, or the inner bull, and bring you to exactly zero. That is why players try to leave an even number such as 40 (double 20) or 32 (double 16).
4. Bust rules
A turn is a bust if your score would go below zero, would be left on exactly 1 (no double can finish 1), or would reach zero with a dart that is not a double. The whole turn counts as zero and you keep the score you had before the turn.
5. Double in (optional)
Some leagues also play double in: your score only starts counting after you hit a double. Darts before that first double do not count.
6. Legs and sets
A game of 501 to zero is one leg. Matches are usually first to a number of legs (for example best of 5 means first to 3). In sets play, legs are grouped into sets.
7. Who throws first
The first thrower usually alternates every leg, so each player starts the same number of legs.
Scoring 501 with Ochepad
Ochepad does the subtraction and the bust check for you. Type the three-dart total, or enter each dart as single, double or treble, and it applies double out, straight out or double in as you chose. It shows a checkout route when you are on 170 or less, switches the first thrower every leg, saves every turn and lets you fix any turn later. No ad appears while you are entering scores.
FAQ
Does the bullseye count as a double in 501?
Yes. The inner bull (50) counts as a double, so you can finish on 50 with the bull.
What happens to my score when I bust?
The whole turn is void. Your remaining score goes back to what it was at the start of that turn, and the next player throws.
What is straight out?
A casual variant where any dart that hits exactly zero wins, double or not. It is faster for beginners and children.
Get Ochepad, a darts scoreboard that handles double out and busts (Google Play)