Fixture Unit Calculator (Drainage Load)

Drainage load is not measured in gallons - it is measured in fixture units, a shorthand that lets codes size a whole branch from the fixtures connected to it. A toilet and a floor drain cannot be added as flows, but they can be added as load.

Fixture Unit Calculator tallies common fixtures into a total drainage load and shows which pipe sizes can carry it.

• Common fixtures: Toilets, bathtubs, showers, lavs, sinks, laundry.
• Live totals: DFU updates as you count.
• Size preview: Minimum drain sizes the load supports.
• Breakdown: See which fixtures dominate the load.
• Export: Copy or download the report.

1. Count each fixture type on the branch, logical group, stack or building.
2. Read the total DFU immediately.
3. Check the size preview for horizontal, stack and building drain.
4. Copy the total into a sizing tool or report.

Example - Single bathroom. Toilet (3) + shower (2) + double lav (2) + tub (2) = 9 DFU. The branch deserves 2 in; the building drain can carry 9 DFU in 2 in too, but a 3 in stack is the familiar residential choice.

• Fast load building: count and go.
• House or restaurant: mix public and private fixtures.
• Feeds every sizing table: same DFU total, four contexts.
• Free and private: no uploads, no logging.