What is the Hunter's Curve?

It is the standard probability curve that converts a building's total fixture units into a realistic simultaneous peak demand in gallons per minute. Not every fixture runs at once, so the curve flattens sharply as fixture count rises.

Why apply a two-thirds rule to the meter capacity?

AWWA M22 advises sizing so normal peak demand does not exceed about two-thirds of a displacement meter's maximum continuous flow. Running a meter near its ceiling continuously increases head loss and accelerates wear.

What meter sizes does this cover?

It covers the common residential and light-commercial displacement meters: 5/8 inch, 3/4 inch, 1 inch, 1.5 inch, and 2 inch, with rated maximum continuous flows of 20, 30, 50, 100, and 160 GPM respectively.

What if my demand exceeds a 2 inch meter?

Loads above roughly 100 GPM of safe capacity call for a compound or turbine meter, a 3 inch or larger service, or a dual-meter arrangement. The tool flags this case rather than recommending an undersized meter.

Does fire flow get added to this?

No. This sizes the domestic service for normal occupancy demand only. Fire sprinkler and hydrant demand are sized separately and usually fed through a dedicated fire service and meter or a combined detector-check assembly.

Water Service Meter Sizing Calculator

A water meter that is too small chokes the whole building with head loss, while one that is too large is more expensive and meters low flows inaccurately. This calculator follows AWWA M22 practice: it converts your total fixture-unit load to a realistic peak demand and then picks the smallest meter that can carry it with a safe margin.

How it works

Two steps produce the recommendation:

peak GPM        = Hunter's Curve( total WSFU )
required rating = peak GPM ÷ (2/3)   = peak × 1.5
meter           = smallest AWWA meter with max flow ≥ required rating

The Hunter’s Curve captures the fact that fixtures rarely run simultaneously, so a 60 WSFU load produces roughly 27 GPM rather than the sum of every fixture’s flow. Dividing by two-thirds keeps the chosen meter operating below its continuous-flow ceiling.

Example and tips

A small commercial building totalling 60 WSFU yields about 27 GPM of peak demand. Required rated capacity is 27 ÷ (2/3), or roughly 41 GPM, so a 1 inch meter rated at 50 GPM is selected; a 3/4 inch meter at 30 GPM would be overloaded. Always size to your local fixture-unit table, since some jurisdictions weight flush valves and continuous-flow fixtures differently, and add any irrigation or process load that runs at the same time as domestic use.