How long should a ramp be for a 3 foot rise?

I'm curious, when it comes to constructing a ramp for a 3-foot rise, what would be the ideal length? I'm aware that ramp length is crucial for accessibility and safety, but I'm not sure how to calculate it accurately. Could you provide some guidance on determining the appropriate ramp length for a 3-foot vertical rise, taking into consideration factors such as slope, space constraints, and user needs?