Calculate drainage runoff, flow rate, runoff volume, pipe capacity, drainage time, slope, and water removal needs. Use this drainage calculator for yards, fields, gardens, trails, driveways, swales, ditches, culverts, rain events, stormwater planning, and outdoor drainage estimates.
Runoff volume:
The calculator multiplies drainage area, rainfall depth, and runoff coefficient to estimate how much water needs to drain.
Peak flow:
Use drainage area, rainfall intensity, and runoff coefficient to estimate peak runoff flow.
Pipe capacity:
Enter pipe diameter and water velocity to estimate drain or culvert flow capacity.
Drain time:
Enter a known water volume and flow rate to estimate how long drainage may take.
A drainage calculator helps estimate runoff volume, flow rate, pipe capacity, and drainage time before choosing drains, pipes, swales, ditches, or runoff controls.
It can be useful for yards, gardens, driveways, fields, trails, culverts, stormwater channels, low spots, pond overflow, roof runoff, and outdoor water management.
Your result shows estimated runoff volume, peak drainage flow rate, pipe capacity, gallons, cubic feet, acre-feet, gallons per minute, cubic feet per second, drainage time, and whether the entered pipe capacity may meet the estimated runoff demand.
Multiply drainage area by rainfall depth and runoff coefficient. The runoff coefficient estimates how much rainfall becomes runoff instead of soaking into the ground.
A runoff coefficient is a factor between 0 and 1. Higher values mean more water runs off the surface, such as pavement or roof areas.
Calculate pipe area from diameter, then multiply by water velocity. This gives flow in cubic feet per second when area is in square feet and velocity is in feet per second.
Actual drainage can be reduced by sediment, leaves, roots, flat slope, clogged grates, undersized outlets, compacted soil, standing water, ice, and pipe friction.