Rational method runoff coefficients are tabulated below. Note that Stormwater Studio allows you to compute composite coefficients with up to three pairs of drainage area and coefficients.
| Description of Area | Coefficient | Typical Design |
|---|---|---|
| BUSINESS | ||
| Downtown | 0.70 - 0.95 | |
| Neighborhood | 0.50 - 0.70 | |
| RESIDENTIAL | ||
| Single family | 0.35 - 0.45 | |
| Multi-units detached | 0.40 - 0.75 | |
| Suburban | 0.25 - 0.40 | |
| Apartments | 0.50 - 0.70 | |
| INDUSTRIAL | ||
| Light | 0.50 - 0.80 | |
| Heavy | 0.60 - 0.90 | |
| Parks, Cemeteries | 0.10 - 0.25 | |
| Playgrounds | 0.20 - 0.35 | |
| Railroad yards | 0.20 - 0.40 | |
| Lawns, sandy soil | 0.05 - 0.20 | |
| Lawns, heavy soil | 0.18 - 0.35 | 0.30 |
| Unimproved | 0.10 - 0.30 | 0.30 |
| Asphalt | 0.70 - 0.95 | 0.90 |
| Concrete | 0.80 - 0.95 | 0.90 |
| Roofs | 0.75 - 0.95 | 0.90 |