1-1/2" Diameter Min Code Fall: 1/4" per foot 2.08% Grade (1:48) IPC Table 704.1

1-1/2" Drain Pipe Slope & Fall Calculator

Under model plumbing codes (IPC & UPC), a horizontal 1-1/2" gravity drainage pipe must be installed with a minimum fall of 1/4" per foot (2.08% pitch or 1:48 slope ratio) to ensure self-scouring velocity (2.0 ft/s). Part of our master Drain Pipe Slope Calculator and Flow Rate Calculator suite.

Presets:

Slope Profile 1.67% Grade

Calculated Drain Slope

2.08% 1 : 48.0

Equivalent Fall: 1/4" per foot (2.50" per 10 ft)

Total Fall (Drop) 5.00 in

Horizontal Run 20.00 ft

Fall per Foot 0.250 in/ft

Actual Cut Length 20.00 ft

Your drain pipe drops 5.00 inches over a 20.00 ft horizontal run. This produces a 2.08% slope (1 : 48.0 ratio), dropping 0.250 inches per foot (2.50 inches per 10 feet).

Code Elevation Drop Schedule

1-1/2" Drain Pipe Fall vs. Run Length Chart

Exact elevation drop required over distance at standard 1/4" per foot slope (2.08% grade).

Horizontal Run (Ft)	Required Drop (Inches)	Ft-Inches Format	Metric Fall (mm)	Code Compliance Status
5 ft	1.25 in	0' 1.3"	31.7 mm	✓ Meets IPC/UPC
10 ft	2.50 in	0' 2.5"	63.4 mm	✓ Meets IPC/UPC
15 ft	3.75 in	0' 3.8"	95.1 mm	✓ Meets IPC/UPC
20 ft	5.00 in	0' 5.0"	126.8 mm	✓ Meets IPC/UPC
30 ft	7.50 in	0' 7.5"	190.2 mm	✓ Meets IPC/UPC
40 ft	10.00 in	0' 10.0"	253.6 mm	✓ Meets IPC/UPC
50 ft	12.50 in	1' 0.5"	317.0 mm	✓ Meets IPC/UPC
75 ft	18.75 in	1' 6.8"	475.5 mm	✓ Meets IPC/UPC
100 ft	25.00 in	2' 1.0"	634.0 mm	✓ Meets IPC/UPC

Plumbing Code Compliance

IPC & UPC Code Rules for 1-1/2" Sanitary Piping

Regulatory parameters, maximum fixture unit capacities, and velocity thresholds.

Minimum Code Slope
1/4" per foot
2.08% Grade (1:48)

Drop Per 10 Feet

2.5 inches

Elev. delta per 10ft stick

Drop Per 50 Feet

12.5 inches

Total fall for 50ft run

Max Drainage Fixture Units

3 DFU

At minimum allowable slope

Min Scouring Velocity

2 ft/sec

Self-cleaning threshold

Governing IPC Reference

Table 704.1

International Plumbing Code

Primary Fixtures Connected to 1-1/2" Drains:

Bathroom lavatory sinks
Bidet waste outlets
Bathtub trap arms
Kitchen sink single branches

Trade Installation Advisory: Standard minimum slope requirement for residential 1-1/2" fixture waste pipes connecting trap arms to branch vents.

Pipe Diameter Navigation

Compare Slope Requirements for Other Pipe Sizes

Explore sanitary fall and grade rules across different drain diameters.

Master Engine Drain Pipe Slope Calculator Larger Drain → 2" Drain Pipe Slope

Expert FAQ Guide

1-1/2" Drain Pipe Slope FAQs

Code questions and fall calculations for 1-1/2" sanitary drainage piping.

3 Questions Answered

Q1 What is the minimum code slope for 1-1/2" drain pipe?

Both the International Plumbing Code (IPC Table 704.1) and Uniform Plumbing Code (UPC) require a minimum slope of 1/4 inch per foot (2.08% grade or 1:48 fall ratio) for 1-1/2" horizontal drainage piping.

Q2 How much should a 1-1/2" drain drop over 10 feet?

At the standard 1/4" per foot slope, a 1-1/2" drain pipe must drop exactly 2.5 inches (63.5 mm) over a 10-foot run.

Q3 Can you slope a 1-1/2" drain pipe at 1/8" per foot?

No. Plumbing codes strictly prohibit 1/8" per foot on pipes 2-1/2" or smaller because lower velocity allows grease, soap scum, and solids to settle, causing chronic clogs.

1-1/2" Drain Pipe Fall vs. Run Length Chart

IPC & UPC Code Rules for 1-1/2" Sanitary Piping

Primary Fixtures Connected to 1-1/2" Drains:

Compare Slope Requirements for Other Pipe Sizes

1-1/2" Drain Pipe Slope FAQs

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