The formula
strike = 10 + the next two throws · spare = 10 + the next throw
Where it comes from
What makes bowling scoring unusual is that a strike is not worth ten: it is worth ten plus whatever comes next. That is why a frame cannot be scored until the throws that close it have been made, and why a perfect game is three hundred and not a hundred and twenty. Twelve strikes in a row — ten frames plus the two bonus throws of the tenth — give thirty points in every frame, and that is where the round number comes from.
How to work it out by hand
- Write down the pins knocked down on each throw, in order
- If a frame is a strike, add ten plus the next two throws
- If it is a spare, add ten plus the next throw
- If it stays open, add what fell and move on
What is worth knowing
The tenth frame gets two or three throws depending on what happens: a strike on the first earns two more, and a spare on the first two earns one. It is not an arbitrary exception, it is what the last frame needs so its bonus has throws to count. Average per frame is the figure that compares games of different lengths, and for a casual bowler it sits between thirteen and seventeen: two hundred points is already league standard.