Plumbing Fixture Flow Calculator
Estimate total connected plumbing-fixture flow and a preliminary simultaneous-use flow from editable fixture counts, individual rates and a diversity factor.
Default project preview
9.6 gpm
Shower connected flow
4 gpm
Faucet connected flow
6 gpm
Toilet-fill connected flow
6.6 gpm
Other connected flow
2.5 gpm
Calculator
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Input and output guide
What each value means
The labels and units below are part of this calculator’s visible methodology. Replace every default with measurements or product data from the actual project.
Showers
Enter this project assumption in a unitless value. The current imperial default is 2. Minimum: 0.
Flow per shower
Enter this project assumption in gpm. The current imperial default is 2 gpm. Minimum: 0.
Faucets
Enter this project assumption in a unitless value. The current imperial default is 4. Minimum: 0.
Flow per faucet
Enter this project assumption in gpm. The current imperial default is 1.5 gpm. Minimum: 0.
Toilet fill valves
Enter this project assumption in a unitless value. The current imperial default is 3. Minimum: 0.
Flow per toilet fill valve
Enter this project assumption in gpm. The current imperial default is 2.2 gpm. Minimum: 0.
Other flowing fixtures
Enter this project assumption in a unitless value. The current imperial default is 1. Minimum: 0.
Flow per other fixture
Enter this project assumption in gpm. The current imperial default is 2.5 gpm. Minimum: 0.
Simultaneous-use factor
Enter this project assumption in %. The current imperial default is 50 %. Minimum: 1. Maximum: 100.
How to read the outputs
Shower connected flow
2 showers. Default preview: 4 gpm.
Faucet connected flow
4 faucets. Default preview: 6 gpm.
Toilet-fill connected flow
3 fill valves. Default preview: 6.6 gpm.
Other connected flow
1 other fixture. Default preview: 2.5 gpm.
Diversified hourly volume
if sustained for one hour. Default preview: 573 gal/h.
Diversified flow per second
same planning flow. Default preview: 0.159 gal/s.
Methodology
Transparent calculation
BuildMeter converts every input to a consistent internal unit, applies the selected allowance, and rounds products up to whole purchasable units.
Connected flow = sum of fixture count × entered fixture flow. Preliminary simultaneous flow = connected flow × simultaneous-use factor.
Reviewed project guidance
How to use this estimate in a real project
Last reviewed: July 30, 2026
Use the Plumbing Fixture Flow Calculator to estimate a planning quantity from verified fixture flow rates, simultaneous use and operating duration. It supports scope comparison, purchasing and operating-cost planning, but it does not select equipment, approve code compliance or replace project-specific design.
Calculation steps
- 1Measure or obtain each design input from the actual project and keep one consistent unit system.
- 2Enter fixture flow rates, simultaneous use and operating duration using product data or approved design information rather than generic nominal values.
- 3Review the unrounded engineering or usage result before applying allowances, duty cycle, efficiency or tariff assumptions.
- 4Apply each adjustment once, then round only the final purchasing, equipment-count or scheduling output.
Worked numerical example
Two 1.5 gpm fixtures and one 2.0 gpm fixture running simultaneously create a direct connected flow of 5.0 gpm before any diversity assumption.
Purchasing and rounding
Use rated fixture flow and a justified simultaneity assumption for the planning question. Pipe sizing and service sizing must follow the applicable plumbing method rather than simply adding every fixture rating.
Interpret the result
The output is simultaneous flow under the assumptions entered. It is different from fixture-unit demand methods and does not include pressure loss through piping, valves or elevation.
Page-specific assumptions
- Inputs describe the actual connected system or measured project scope.
- One operating condition, product rating and unit system are used per calculation.
- Allowances and efficiency losses are not already embedded in the entered values.
- Code, health, structural, electrical and hydraulic requirements are verified independently.
Common mistakes
- Using nominal equipment ratings instead of delivered performance at design conditions.
- Mixing instantaneous flow or power with daily or annual energy.
- Applying the same allowance more than once.
- Treating a quantity or cost estimate as equipment selection or professional approval.
Primary and technical references
BuildMeter provides planning estimates, not engineering, architectural, electrical, mechanical, plumbing, permit or code approval. Review the methodology and verify final decisions with product documentation and qualified professionals.
BuildMeter Guides
Understand the measurements and assumptions
Use these visible reference guides before changing project inputs or planning allowances.
FAQ
Plumbing Fixture Flow Calculator questions
Is connected flow the expected normal demand?+
No. It represents every entered fixture flowing at once. The diversity factor creates a simpler simultaneous-use planning value.
Can this replace a fixture-unit calculation?+
No. Plumbing codes and utility requirements may use fixture units, pressure and developed length rather than a simple percentage.
Why include toilet fill-valve flow?+
A toilet can draw water while refilling, although the duration and actual fill-valve rate vary.