How does the peak flow calculator work?

It first finds the average flow by dividing your daily water demand by the supply window in minutes — that is hours multiplied by 60. It then multiplies that average by a peak factor to get the peak, or design, flow because fixtures cluster at the morning and evening rush rather than running evenly all day. The result is shown in both litres per minute and litres per second.

What inputs do I need and what values are sensible?

You need three things: daily water demand in litres, the hours over which it is drawn, and a peak factor. For homes, demand is often people multiplied by 135 litres per person per day, so ten people is about 1,350 litres. Supply windows are commonly 6 to 8 hours, and a peak factor of about 2.5 to 3 is typical for residential use. Adjust each value to match your building.

How accurate is the peak flow, and what should I verify?

Treat the number as indicative sizing for concept planning, not a final design. It uses a simple peak-factor method, so it can differ from a detailed fixture-unit or Hunter analysis, which counts individual taps and their likelihood of running together. For pipe and pump procurement, especially in larger buildings, confirm the design flow with a qualified plumbing consultant and check requirements against NBC 2016 Part 9.

Interactive Calculator · 2026

Peak Flow Calculator

Estimate the peak — or design — flow rate to size supply pipes and pumps. Enter the daily water demand, the hours over which it is drawn and a peak factor, and get the average flow plus the peak flow in both L/min and L/s.

Peak design flow (at ×3 peak factor)0.00 L/min≈ 0.00 L/s · average 2.81 L/min

Average flow → peak flow (with the peak factor applied)

Your demand profile

Daily water demand (L/day)

Total volume the supply must deliver in a day — e.g. 10 people × 135 LPCD ≈ 1,350 L/day.

Supply / usage hours per day8 hr

The window over which that demand is actually drawn — shorter windows concentrate the flow.

Peak factor×3

Multiplier that captures how fixtures cluster at morning and evening peaks — 2.5–3 is typical for residential.

Average flow

0.00 L/min

Peak flow

0.00 L/min

Peak flow

0.00 L/s

Average flow vs peak flow

Pipes and pumps must be sized for the peak, not the daily average.

The average flow assumes water is drawn steadily all day. In reality fixtures fire together at the morning and evening rush, so the design flow is the average lifted by the peak factor — here 8.44 L/min (0.14 L/s).

Size the supply pipe and pump for this peak so taps do not starve at the busiest hour.

How this is calculated

Average flow = daily demand ÷ (hours × 60) = 1,350 ÷ (8 × 60) = 2.81 L/min.
Peak flow = average flow × peak factor = 2.81 × 3 = 8.44 L/min.
Peak flow (L/s) = peak flow ÷ 60 = 8.44 ÷ 60 = 0.14 L/s.

The peak factor captures the fact that fixtures cluster at the morning and evening peaks rather than running evenly all day. This is indicative sizing for concept planning — verify with a fixture-unit (Hunter) method and confirm with a qualified consultant or NBC 2016 Part 9 before procurement, especially for larger buildings.

Understand the number you just got

Water Supply Systems in IndiaHow buildings store, pump and distribute water from source to tap.Building Plumbing Services GuideThe full picture of supply, drainage, venting and services design.

Frequently asked questions

How does the peak flow calculator work?: It first finds the average flow by dividing your daily water demand by the supply window in minutes — that is hours multiplied by 60. It then multiplies that average by a peak factor to get the peak, or design, flow because fixtures cluster at the morning and evening rush rather than running evenly all day. The result is shown in both litres per minute and litres per second.
What inputs do I need and what values are sensible?: You need three things: daily water demand in litres, the hours over which it is drawn, and a peak factor. For homes, demand is often people multiplied by 135 litres per person per day, so ten people is about 1,350 litres. Supply windows are commonly 6 to 8 hours, and a peak factor of about 2.5 to 3 is typical for residential use. Adjust each value to match your building.
How accurate is the peak flow, and what should I verify?: Treat the number as indicative sizing for concept planning, not a final design. It uses a simple peak-factor method, so it can differ from a detailed fixture-unit or Hunter analysis, which counts individual taps and their likelihood of running together. For pipe and pump procurement, especially in larger buildings, confirm the design flow with a qualified plumbing consultant and check requirements against NBC 2016 Part 9.

Related Guides — Deep-dive reading

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