WATER METER SIZE
WATER METER SIZE
meter ≥ peak GPM at acceptable Δp
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AWWA M22-based residential meter sizing. Always confirm with your local water utility — they set the actual service size. Estimate only — verify with a licensed plumber and local plumbing code/inspector before purchase or installation. Not a substitute for engineered drawings.
About this calculator
This water meter size calculator returns the recommended residential or small commercial water meter based on total fixture units, using the AWWA M22 sizing approach. Meters that are too small choke peak flow and cause pressure complaints; meters that are too large under-register low flows and cost the utility (and you, on a per-meter charge). The output gives the displacement-meter size with safe margin, plus the peak GPM that meter is rated for so you can sanity-check against fixture demand. ESTIMATE ONLY — verify with a licensed plumber and local plumbing code before installation.
Common questions
How does the utility decide my water meter size?
Most utilities use the AWWA M22 method: estimate peak demand from fixture units (or a flat per-unit value for multi-family), then pick the smallest meter that handles the peak with 15–20% margin. They'll oversize cautiously because under-sized meters cause customer complaints they have to fix. The most common residential meter in the US is a ⅝" × ¾" displacement meter, which handles 10 GPM continuous and 20 GPM intermittent — enough for a typical 2-bath home.
What size meter do I need for a tankless water heater?
Most whole-home tankless heaters pull 7–11 GPM at full output. A ⅝" × ¾" meter (10 GPM continuous) is borderline; a ¾" meter (15 GPM) gives proper headroom. If your house already has a ⅝" meter and you install a tankless that pulls 9 GPM, expect noticeable pressure dip during simultaneous shower and dishwasher use. Coordinate with the utility about a meter upsize before committing to the install.
Why not just install the biggest meter possible?
Three reasons. (1) Cost: bigger meters carry higher monthly base fees in most utility tariffs. (2) Accuracy at low flow: a 2" meter has a minimum registration threshold around 1.5 GPM, which means a slow toilet leak doesn't register and you don't get billed for it (sounds great, but the utility tariff sets your fixed cost based on meter size to recover this). (3) Service line cost: bigger meters need bigger service lines, which means more excavation and more pipe.