Calculate drain pipe slope, pipe fall and total drop in seconds — automatically checked against IPC, UPC and NPC minimum slopes. Or lay your iPhone on the pipe and measure the grade directly.
Scan with your iPhone camera to download
Built for plumbers, pipefitters, contractors and inspectors — and precise enough for the serious DIYer roughing in a bathroom.
Enter length + drop to get the slope, or length + slope to get the required total drop. Results in in/ft, mm/m and percent grade.
Select IPC, UPC or NPC and the app flags any slope below the minimum for your pipe size — including the UPC's 4"+ AHJ exception.
Digital torpedo level mode: lay the phone along the pipe, watch the live reading turn green at your target slope, then capture it into the calculator.
Basements, crawl spaces, new builds with no service — every feature works with zero signal. No account, no ads, no tracking.
Save up to 50 calculations with custom titles. Restore yesterday's main-line numbers in one tap, or copy full results to paste into a text or report.
1½" through 15" (DN 40–DN 375), with common slope presets from 1/16"/ft to 1"/ft and a slider for any custom grade.
Swipe through the app — from code selection to slope measurement.
Choose IPC, UPC or NPC and tap your pipe size (1½"–15"). The app instantly knows the minimum slope that applies.
Type the run length and either the drop you have or the slope you want — or capture the live slope by laying your iPhone on the pipe.
Total drop, slope in in/ft or mm/m, percent grade, and a clear warning if you're below the code minimum. Copy or save the result for the job file.
The numbers the app checks for you, straight from the three major North American plumbing codes:
| Pipe size | IPC 2024 (§704.1) | UPC 2024 | NPC 2020 (Canada) |
|---|---|---|---|
| 1½" – 2½" | ¼"/ft (2.08%) | ¼"/ft (2%) | 1:50 · ¼"/ft (2%) |
| 3" | ⅛"/ft (1.04%) | ¼"/ft (2%) | 1:50 · ¼"/ft (2%) |
| 4" – 6" | ⅛"/ft (1.04%) | ¼"/ft (2%)* | 1:100 · ⅛"/ft (1%) |
| 8" – 15" | 1/16"/ft (0.52%) | ¼"/ft (2%)* | 1:100 · ⅛"/ft (1%) |
* UPC: pipe 4" and larger may be approved at ⅛"/ft (1%) by the Authority Having Jurisdiction where ¼"/ft is impractical. Reference only — always verify with your local AHJ. See the full IPC vs UPC vs NPC comparison.
Straight answers to the slope questions plumbers and DIYers actually search for — each with the exact code numbers and a worked example.
IPC, UPC and NPC minimums for every pipe size from 1½" to 15", in one chart.
Read the guide →Fall per foot by pipe size, plus a total-fall chart for runs from 10 to 100 feet.
Read the guide →⅛" or ¼" per foot? What each code requires for 4" main lines — and why it matters.
Read the guide →The size where IPC and UPC disagree. What your toilet drain actually needs.
Read the guide →The formula, percent-grade conversion table, and two worked examples.
Read the guide →Can a drain be too steep? What the codes say and the ¼"–½" field rule.
Read the guide →Drop chart from 1 to 100 feet, plus conversions to percent, mm/m and degrees.
Read the guide →Turn your phone into a digital torpedo level and capture the reading into the calculator.
Read the guide →Side-by-side comparison of the three major codes, including the UPC's AHJ exception.
Read the guide →1:50 vs 1:100, mm per metre, DN pipe sizes and how to convert to percent.
Read the guide →Under the International Plumbing Code (IPC), horizontal drain pipes 2½ inches and smaller need a minimum slope of ¼ inch per foot, pipes 3 to 6 inches need ⅛ inch per foot, and pipes 8 inches and larger need 1/16 inch per foot. The UPC requires ¼ inch per foot for all sizes unless the local authority approves flatter slope on 4-inch-plus pipe. Always confirm with your local code. Learn more →
Most sewer lines need ¼ inch of fall per foot of run for pipes up to 3 inches, and ⅛ inch per foot for 4-inch and larger pipe under the IPC. A 50-foot 4-inch sewer at ⅛ inch per foot drops 6.25 inches in total. Learn more →
A 4-inch sewer or drain pipe needs a minimum slope of ⅛ inch per foot (about 1%) under the IPC and NPC. The UPC requires ¼ inch per foot (2%) unless the Authority Having Jurisdiction approves ⅛ inch per foot. Learn more →
Under the IPC, a 3-inch drain needs at least ⅛ inch per foot of slope. Under the UPC and Canada's NPC, a 3-inch drain needs ¼ inch per foot. Many plumbers run 3-inch toilet drains at ¼ inch per foot regardless, for a self-cleaning safety margin. Learn more →
Divide the total drop by the pipe length. For slope in inches per foot, divide the drop in inches by the run in feet. For percent grade, divide inches-per-foot by 12 and multiply by 100 — so ¼ inch per foot equals about 2.08%. Learn more →
Codes set minimum slopes, not general maximums, and slopes of 45 degrees or steeper are treated as vertical piping. A widely used field guideline keeps gravity drains carrying solids between ¼ and ½ inch per foot, because very steep, shallow-graded runs can let liquids outrun solids. Some local authorities do publish maximum-pitch rules, so check your jurisdiction. Learn more →
At ¼ inch per foot, a 20-foot run drops 5 inches in total. The formula is run in feet × 0.25 inches — for example 10 ft drops 2.5 inches and 40 ft drops 10 inches. Learn more →
Yes. Pipe Slope Calculator uses the iPhone's built-in tilt sensor as a digital torpedo level: place the phone on its side edge along the pipe and read live slope in inches per foot or mm per metre. Sensor readings are approximate (±1–2° / ±0.2 in/ft), so verify with a calibrated level before making code-compliance decisions. Learn more →
The IPC scales minimum slope with pipe size (¼ in/ft up to 2½ inches, ⅛ in/ft for 3–6 inches, 1/16 in/ft for 8 inches and up). The UPC requires ¼ in/ft for all sizes, with a possible ⅛ in/ft exception for 4-inch-plus pipe where the local authority approves. Canada's NPC requires 1:50 (about ¼ in/ft) up to 3 inches and 1:100 (about ⅛ in/ft) for larger pipe. Learn more →
A 1:50 gradient means 1 unit of fall per 50 units of run — 20 mm of fall per metre, or a 2% grade. A 1:100 gradient is 10 mm per metre, or 1%. Multiply the run length by the gradient to get total fall: 8 m at 1:50 falls 160 mm. Learn more →
Yes — the app works 100% offline. Every calculation, code check, slope measurement and saved entry runs on the device, so it works in basements, crawl spaces and remote job sites with no signal. It collects zero personal data and contains no ads or tracking.
Pipe Slope Calculator is a one-time purchase of US$2.99 on the App Store. There is no subscription, no ads, no account and no in-app purchases — you pay once and own it.
Get the right slope, fall and drop — code-checked — before you set the pipe.
Scan with your iPhone camera
US$2.99 one-time · iOS 17+ · iPhone (runs on Apple Silicon Macs too) · 3.3 MB