Garden & Outdoor calculator
What Rainwater Overflow Tank Size Do I Need?
Find overflow buffer tank capacity from peak rainwater inflow, safe overflow/discharge capacity, and design storm duration.
Enter your measurements
What Rainwater Overflow Tank Size Do I Need? Measure peak rainwater inflow, safe overflow/discharge capacity, and design storm duration first. This tool converts them into overflow buffer tank capacity so the recommendation stays tied to your actual dimensions or specification.
- Peak rainwater inflow — Required
- Safe overflow/discharge capacity — Required
- Design storm duration — Required
- Storage reserve fraction — Required
Overflow buffer tank capacity
Enter the measurements above to calculate overflow buffer tank capacity.
How the calculation works
V12 calculation: excessFlow=max(0,incomingPeakFlow-outflowCapacity); stormDurationSeconds=stormDuration×3600; bufferVolume=excessFlow×stormDurationSeconds×(1+reserve). This is the implementation specification for this calculator.
Worked example
Example: Peak rainwater inflow = 1 L/s; Safe overflow/discharge capacity = 0.6 L/s; Design storm duration = 1 h; Storage reserve fraction = 15%. Result: Buffer Volume = 1656 L; Storm Duration Seconds = 360000%; Excess Flow = 0.4 L/s.
Before you decide
Recheck the limiting measurement before purchase or installation. This page calculates the stated geometry or quantity only; product-specific construction or installation details can still affect the final choice. For what rainwater overflow tank size do i need, the limiting result on this page is overflow buffer tank capacity.
Direct measurement/geometry calculation. No external reference is required for the arithmetic itself; the result is derived only from the user-entered measurements and the formula stored in calculationLogicJson.
Frequently asked questions
What does the Rainwater Overflow Tank Size calculator tell me?
It returns overflow buffer tank capacity from the measurements entered on this page. The calculation is specific to rainwater overflow tank size, so the result should be compared with the exact product or specification you are considering.
Which measurements should I take for rainwater overflow tank size?
Measure peak rainwater inflow, safe overflow/discharge capacity, design storm duration, storage reserve fraction. Use clear, usable dimensions rather than nominal room or product labels.
Should I round the overflow buffer tank capacity?
Keep the calculated value for comparison, then choose a real product that meets or stays within the returned overflow buffer tank capacity while allowing for the clearances, tolerances or ratings shown by its manufacturer.