The values for ‘mild’, ‘moderate’ and ‘severe’ urinary incontinence have not been determined for the 24-hour pad test. To define these values, a prospective observational study was performed on 110 women with the primary symptom of urinary incontinence. Consenting women performed two 1-hour pad tests one week apart, and seven 24-hour pad tests for seven consecutive days. The 1-hour pad test definitions for mild, moderate and severe were translated to centiles, and used to categorise the 24-hour test values. This revealed that the range for ‘mild incontinence’ was between 1.3 and 20 g, ‘moderate incontinence’ ranged from 21 to 74 g, and ‘severe incontinence’ was defined as 75 g or more in 24 hours. Severity of leakage was analysed in relation to urodynamic diagnosis, age, parity and pelvic floor muscle strength. Increasing severity was associated with increasing age and parity. Women with detrusor overactivity were most likely to have severe leakage. In conclusion, this study defines the three grades of severity for the 24-hour pad test, which may help to guide patients' choice between conservative and surgical treatment and is useful for stratified randomisation of controlled trial participants.