From this site

One project, every trade

Each calculator adds its lines to a single estimate — consolidated BOM, schedule and cash-flow included.

Open My Project →

Greywater Collection Cistern Peak Inflow Calculator

Calculate the peak inflow rate a greywater collection cistern must handle, from average daily flow and a peaking factor.

Computed in your browser — nothing you enter is uploaded. Figures are presented for United States against IRC 2024, and every formula is cited under regulatory standards below.

Last verified 2026-08-26 · v1.0.0

Market
Imperial · sales tax

Peak inflow rate

1250 L/day

Check your inputs

Peaking factor depends on the building's occupancy pattern and fixture usage profile — confirm the appropriate factor for your specific application against local greywater reuse code requirements.

Running these inputs gives 1250 L/day as the peak inflow rate. Expect some drift against the real job; the calculation is solid but conditions on site are not. Currently reading for United States under IRC 2024 — pick a different market above and the figures re-cast accordingly.

Add the equipment this sizes

This result is a specification — 1,250 L/day — not a quantity. Put the thing it sizes into your project: how many, what you call it, and your supplier’s price.

Preliminary estimate, not certified engineering. This tool produces an indicative quantity calculation for planning purposes only — it is not a certified structural analysis, a guaranteed material takeoff, or a substitute for building department approval. Always verify measurements on-site and have a licensed contractor or structural engineer review any load-bearing, code-sensitive, or safety-critical work before purchasing materials or starting construction. Spotted an arithmetic or standards error? Report it to contact@craftquantities.com with your inputs — confirmed fixes become pinned regression tests.

[Schema Verified] Computed in alignment with American Concrete Institute (ACI 318-19) formulas and International Residential Code (IRC 2024) spatial boundaries.

Regulatory standards & verification citations

  • Peak inflow rate = average daily flow × peaking factor, the standard method for sizing detention/collection systems to handle short-duration peak demand rather than just the daily average

Your workspace

Most jobs need more than one number. Add the calculators you need next and they open right here, underneath this one — your figures stay on screen and nothing is lost to a page change.

Frequently asked questions

Why size the cistern for a peak rate instead of the daily average?
A collection/detention system has to handle the short-duration surges in greywater generation — for example, several showers or a laundry cycle running close together — not just the smoothed-out daily average, so peak inflow rate is the standard basis for sizing.
What peaking factor should I use?
Peaking factor depends on the building's occupancy pattern and fixture usage profile. Confirm the appropriate factor for your specific application against local greywater reuse code requirements rather than assuming a single universal value.
Does this account for local greywater reuse code requirements?
No — this calculator only scales your average daily flow by the peaking factor you provide. The appropriate peaking factor, and any additional sizing margins, must be confirmed against your local greywater reuse code.