Ensure your guttering can handle the water velocity in your area.
Our online calculator will enable you to choose the correct size guttering for your needs in order to prevent overflow which can lead to costly building damage.
Calculate Gutter Flow Rate Velocity
Catchment Area:
Rainfall Intensity:
Flow Rate: 0
How to Use
- Unit System: Choose your preferred unit system (Metric or Imperial).
- Catchment Area: Measure the length and width of your roof or the section that drains into the gutter.
- Rainfall Intensity: The average or peak rainfall intensity for your location.
- Calculate: Show how much water your gutter system needs to handle during heavy rainfall.
Calculator checked on By Jamie
Calculations Used
| Catchment Area | Catchment Area (m² or ft²) = Length × Width |
| Rainfall Intensity | Rainfall Intensity (mm/hr or in/hr) |
| Metric Flow Rate Calculation | Flow Rate (L/s) = (Catchment Area (m²) × Rainfall Intensity (mm/hr)) / 3600 |
| Imperial Flow Rate Calculation | Flow Rate (GPM) = (Catchment Area (ft²) × Rainfall Intensity (in/hr)) / 96.23 |
| Conversion Factor (Metric) | 3600 (seconds in an hour) |
| Conversion Factor (Imperial) | 96.23 |
What is Gutter Flow Rate?
Gutter flow rate refers to the volume of water that a gutter system can effectively handle and channel away from a roof over a specific period, typically measured during heavy rainfall.
It is usually expressed in litres per second (L/s) in the metric system or gallons per minute (GPM) in the imperial system.
The gutter flow rate is crucial for ensuring that your gutter system is adequately sized to prevent overflow and potential water damage to your home's structure, foundation, and landscaping.
Frequently Asked Questions
How can I find the rainfall intensity?
You can find this data from local weather stations, meteorological websites, or building codes for your area.
What should I do if my flow rate is too high for my current gutters?
You may need to upgrade to larger gutters/downspouts, or consider a more efficient gutter system.
How does roof pitch affect gutter flow rate calculations?
A steeper roof pitch may direct water faster, which can increase the volume of water entering the gutters at any given point, potentially requiring larger or additional gutters.
Can I use this calculator for both residential and commercial buildings?
Yes. Just ensure that you accurately input the catchment area and rainfall intensity based on the specific roof structure and location.
What if my roof has multiple sections draining into the same gutter?
You should calculate the catchment area for each section and sum them up before using the calculator. This ensures you account for all the water flowing into the gutter.
How often should I clean my gutters?
It's recommended to clean your gutters twice a year - once in the spring and once in the autumn. Regular maintenance helps prevent clogs and ensures that your gutters can handle the calculated flow rate during heavy rains.