CeļvežiRoofing
Roofing · Practical guide

Kā izmantot Gutter Capacity Calculator — estimate gutter capacity for a roof

Estimate design rainwater flow from effective roof catchment area, rainfall intensity and a transparent safety allowance.

Checked 29 August 2026Clear inputs and assumptionsWorks on mobile
Method

Flow in litres per second = area in m² × rainfall in mm/hour ÷ 3,600, with the selected safety allowance applied.

Estimate design rainwater flow from effective roof catchment area, rainfall intensity and a transparent safety allowance. The linked Sellible tool keeps the fields, units and output together so the assumptions can be reviewed before the result is used.

  1. 1

    Determine effective rather than plan roof area where required.

  2. 2

    Use an appropriate local design rainfall intensity.

  3. 3

    Compare calculated flow with a complete gutter and outlet system.

Worked example

Example values and result

These values demonstrate the method; replace them with measurements, rates or file details that match the real task.

Effective roof area
80 m²
Design rainfall
75 mm/hour
Base flow
1.67 L/s
Safety allowance
20%
What the result means

The example produces a planning flow near 2.0 L/s. Final gutter, outlet and downpipe selection must follow local standards and manufacturer capacity data.

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Before you rely on it

Precizitāte un praktiski norādījumi

  • Consider valley discharge and concentrated flows.
  • Check gutter fall, outlet position and downpipe capacity together.
  • Allow for blockage, maintenance and overflow risk.
Avoid these

Common mistakes

  • Sizing only the gutter while ignoring outlets and downpipes.
  • Using annual rainfall instead of design intensity.
  • Assuming a safety factor replaces local drainage design.
Straight answers

Biežākie jautājumi

Is Gutter Capacity Calculator free?

Yes. This calculator or browser utility is free and does not use processing credits.

Can I use this guide and Gutter Capacity Calculator on a phone?

Yes. The guide, inputs, results and calls to action are responsive and keyboard accessible on current phones, tablets and desktop browsers.

Should I order or make a decision from the estimate alone?

No. Consider valley discharge and concentrated flows. Check gutter fall, outlet position and downpipe capacity together. The calculation is a planning aid rather than professional or regulatory approval.

How should I check the result?

Keep the source values and units visible, compare the result with supplier or project information, and retain enough precision until the final purchasing or reporting step.