Spread width is the distance between a vertical spread's strikes. It bounds the structure's outcome span: a credit vertical's worst case is width minus credit, a debit vertical's max gain is width minus debit, and the credit-to-width ratio is the standard measure of whether a premium sale is adequately paid.
Width is also a sizing lever: at the same short strike, a wider spread collects more credit and carries proportionally more worst-case risk, so worst-case-first sizing keeps widths honest automatically. The credit-to-width floor, commonly around 20% for credit verticals, exists because below it the occasional full loss takes too many winners to repay; a condor inherits the same arithmetic on its wider wing.