Whole-house flow calculator

Whole-House Water Filter Flow-Rate Calculator

Estimate simultaneous household flow and compare it with an exact whole-house filter’s documented rated service flow and pressure loss.

What you are calculating

Daily gallons affect capacity and replacement life. Gallons per minute (gpm) describes the short period when several fixtures run together. Whole-house equipment must satisfy both questions.

1 Choose how to estimate the home’s peak demand

Build a fixture scenarioBest when you know what may run togetherUse a measured flowFrom a flow monitor, meter, or timed volume

What could reasonably run at the same time?

Set the count to zero for anything outside the scenario. Every rate is editable.

Shower2.0 gpm is the WaterSense maximum; replace it with the fixture label or measurement.

Count runningGallons per minute each—

Bathroom faucet1.5 gpm is the WaterSense maximum for a labeled bathroom faucet.

Count runningGallons per minute each—

Kitchen faucet2.2 gpm is the federal maximum; use the installed faucet’s rated or measured flow.

Count runningGallons per minute each—

Tub filler or body spraysFlow varies widely. Enter the manufacturer value or measure it.

Count runningGallons per minute each—

Clothes-washer fillUse the appliance documentation or a measured fill rate.

Count runningGallons per minute each—

Outdoor or irrigation demandInclude only if this branch will pass through the filter.

Count runningGallons per minute each—

Other fixture or applianceAdd any treatment-connected demand likely to run at the same time.

Count runningGallons per minute each—

Starting values use EPA WaterSense maximums for labeled showers and bathroom faucets and the federal maximum for kitchen faucets. Actual flow changes with the fixture and flowing pressure, so replace defaults when better property data exists.

2 Set the comparison target

Optional planning allowance 0% means use the scenario exactly; there is no universal required margin

%

Do not compare with “maximum flow” alone.

Use the exact model’s documented rated service flow for the media, cartridge, and operating conditions being proposed.

Check a proposed filter and pressure loss Optional

Rated service flow gpm from exact model documentationFilter pressure drop at this flow psi; use the manufacturer curve or tableDynamic inlet pressure psi while the scenario is flowingOther known pressure losses psi from prefilters, valves, UV, plumbing, etc.Minimum outlet pressure to compare psi; optional property/design requirement

What the flow result means

The result is a planning target for the simultaneous demand scenario you entered. Compare it with the exact model’s documented rated service flow at the relevant media, cartridge and operating conditions—not an unsupported maximum-flow label.

Formula and measurement boundaries

Fixture mode adds the editable flow of every fixture assumed to run at the same time. Measured mode accepts a direct gallons-per-minute result or converts a timed volume to gallons per minute. An optional planning allowance is then applied and shown in the formula.

Starting fixture values are only references. Replace them with fixture labels, manufacturer data or measurements when available. Static pressure and pipe diameter are not flow measurements.

What to verify before selection

treatment objective and exact certified claim;
rated service flow and pressure-drop curve for the proposed configuration;
dynamic inlet pressure and other filters, valves, UV equipment and plumbing losses;
capacity or replacement basis at the calculated flow;
source and drain flow for equipment that backwashes.

Continue with the whole-house filtration research hub and the treatment selection guide.

Decision boundary

A calculated result is a shortlist input, not an installation design.

Verify the water evidence, exact product documentation, pressure and plumbing conditions, and current ownership terms before selection.

Use the selection guide

Publisher boundary: Water System Guide is an independent research publisher, not a manufacturer, dealer, installer, utility or laboratory.