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Calcimator

Drainage Fixture Unit Calculator

Calculate total drainage fixture units and determine required drain, vent, and stack pipe sizes per plumbing code.

Inputs

IPC Table 709.1: water closet = 4 DFU; urinal = 4 DFU per IPC fixture unit table

IPC Table 709.1: lavatory = 1 DFU; kitchen sink = 2 DFU; service sink = 3 DFU

IPC Table 709.1: shower = 2 DFU; requires 2" minimum trap and 2" drain per IPC

IPC Table 709.1: bathtub = 2 DFU; combination tub/shower = 2 DFU; requires 1.5" trap

IPC Table 709.1: clothes washer = 3 DFU; requires 2" standpipe and air gap per IPC 802

Results

Total DFU

22 DFU

Required Drain Size

4 inches

Required Vent Size2 inches
Stack Size3 inches
How to Use This Calculator
  1. Count each fixture type in the building: toilets, sinks, showers, bathtubs, clothes washers, and dishwashers.
  2. The calculator sums up the Total DFU using IPC/UPC fixture unit values for each type.
  3. Review Required Drain Size and Required Vent Size to specify pipe diameters on your plans.
  4. Check Stack Size to size the vertical drain/soil stack serving multiple floors.
  5. Use these results to verify your plumbing plans meet code before permit submittal.

How the result changes with Toilets (Water Closets)

Toilets (Water Closets)Total DFURequired Drain Size
1054 DFU4 inches
35154 DFU4 inches
65274 DFU5 inches
90374 DFU6 inches

What each input means

Toilets (Water Closets)
Number of toilets/water closets. IPC Table 709.1 assigns 4 DFU (drainage fixture units) per water closet. DFU values determine minimum drain and vent pipe sizes.
Sinks (Lavatories)
Number of lavatory sinks. IPC Table 709.1 assigns 1 DFU per lavatory. Each DFU represents approximately 1 gallon per minute of peak drainage flow.
Showers
Number of shower stalls. IPC Table 709.1 assigns 2 DFU per shower. Showers require a minimum 2-inch trap and drain per IPC 912.
Bathtubs
Number of bathtubs. IPC Table 709.1 assigns 2 DFU per bathtub. Combination tub/shower units also count as 2 DFU.
Clothes Washers
Number of clothes washing machines. IPC Table 709.1 assigns 3 DFU per automatic clothes washer. Requires a 2-inch standpipe with an air gap per IPC 802.
Dishwashers
Number of dishwashers. Each counts as 2 DFU.

How this is calculated

Worked example, using the default values

  1. Identify Input Parameters
    4 parameters
    Toilets (Water Closets) = 2, Sinks (Lavatories) = 3, Showers = 2, Bathtubs = 1 = 6 input(s) provided
  2. Calculate Total DFU
    Total DFU
    22 = 22
  3. Calculate Required Drain Size
    Required Drain Size
    4 = 4
  4. Calculate Required Vent Size
    Required Vent Size
    2 = 2
  5. Calculate Stack Size
    Stack Size
    3 = 3

Engine last updated . Checked against 2 independently-derived tests — how we verify calculators.

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