Roofing, Insulation & Exterior calculator
Gutter Calculator
Estimate roof-runoff flow demand from catchment area and local design rainfall for preliminary gutter sizing.
Estimate roof-runoff flow demand from catchment area and local design rainfall for preliminary gutter sizing. For a reliable estimate, measure the real project rather than relying on nominal room or product sizes. The input most worth checking is catchment area and rainfall intensity. Rainfall intensity and drainage design criteria vary by location. Treat the result as preliminary sizing guidance and check local standards or manufacturer tables.
What you need to enter
The Gutter Calculator uses the following project information to calculate the result.
- Roof catchment area
- Design rainfall intensity
- Gutter run
Calculator result
Flow demand and sizing guidance
How the Gutter Calculator works
To produce flow demand and sizing guidance, the Gutter Calculator applies estimator only; local design standards may govern final sizing. The engine is configured for indicative gutter flow demand from roof catchment and rainfall intensity, not as a generic text estimate. Check catchment area and rainfall intensity, since an incorrect value there can materially change the result.
Gutter Calculator worked example
Gutter Calculator example: For indicative gutter flow demand from roof catchment and rainfall intensity, enter the roof catchment area and the design rainfall intensity for the location. The calculator converts those into a preliminary drainage flow demand, which can then be checked against the chosen gutter or downspout manufacturer's capacity tables. The worked figure becomes more useful when catchment area and rainfall intensity is taken from the real product or site rather than a generic default.
Important calculation assumptions
For indicative gutter flow demand from roof catchment and rainfall intensity, rainfall intensity and drainage design criteria vary by location. Treat the result as preliminary sizing guidance and check local standards or manufacturer tables.
Frequently asked questions
How can I prepare the job data for the Gutter Calculator?
For indicative gutter flow demand from roof catchment and rainfall intensity, enter roof catchment area and a design rainfall intensity appropriate to the location. Use gutter run only where the sizing method requires it. This keeps the calculation tied to the actual job rather than a generic assumption.
How should I handle catchment area and rainfall intensity in the Gutter Calculator?
Do not chase extra decimal precision in the Gutter Calculator until you have realistic values for catchment area and rainfall intensity. Rainfall intensity and drainage design criteria vary by location. Treat the result as preliminary sizing guidance and check local standards or manufacturer tables.
What drainage checks follow the Gutter Calculator result?
For the Gutter Calculator, use the flow demand to shortlist gutter sizes, then verify capacity against local design rainfall and the manufacturer's hydraulic tables. This keeps the estimate connected to the actual product, site or design.