Roof Pitch Calculator
Calculate roof pitch as the standard "X/12" ratio, angle, slope percent, and the rafter length multiplier from a measured rise and run — plus how your pitch compares to common named roof slopes.
Input
Set this to 12 to read the pitch straight off as "rise/12" — the standard roofing convention. Enter your roof's actual horizontal run instead to also get the real rafter length.
Purely cosmetic — rise and run must already share the same unit.
Output
| Property | Value |
|---|---|
| No data yet | |
| Pitch | Angle | Notes / Your Roof |
|---|---|---|
| No data yet | ||
How your roof's pitch compares to a few widely used named roof slopes.
More ways to use this tool
REST API
curl -X POST https://api.iotools.cloud/v1/tool/roof-pitch-calculator \
-H "Authorization: Bearer YOUR_API_KEY" \
-H "Content-Type: application/json" \
-d '{
"rise": "6",
"run": "12",
"unit": "in"
}'Swap in your own key from your account. The tool's fields are the body — no wrapper.
Ask an AI agent
Use the IOTools `roof-pitch-calculator` tool (Roof Pitch Calculator) on this input:
YOUR_INPUT_HEREPaste this at any agent connected to the IOTools MCP server, then add your input.
Embed widget
<iframe
src="https://iotools.cloud/embed/roof-pitch-calculator/"
width="100%" height="520" frameborder="0" scrolling="no" loading="lazy"
title="Roof Pitch Calculator — iotools.cloud"
sandbox="allow-scripts allow-forms allow-same-origin allow-downloads allow-popups allow-popups-to-escape-sandbox"
allow="clipboard-write"
style="width:100%;border:1px solid #e5e7eb;border-radius:12px;overflow:hidden"></iframe>
<script src="https://iotools.cloud/embed.js" async></script>Drop this into your own page — free, no key required, just a link back.
| Cost per API/MCP call | From 5 credits |
|---|
Also available with
Guides
The Roof Pitch Calculator turns a measured rise and run into the numbers a roofer or framer actually uses: the pitch expressed as the standard "X/12" ratio, the roof angle in degrees, the slope percentage, and the rafter length multiplier — a single number you multiply your horizontal run by to get the actual rafter length, instead of working out the hypotenuse by hand every time.
How to use it
- Enter the rise — how much the roof climbs vertically.
- Enter the run — the horizontal distance it climbs over. Set this to 12 to read the pitch straight off as "rise/12," the way roof pitches are conventionally described in the US. Enter your roof's actual horizontal run instead (e.g. half the building's width) to also get the real rafter length you'll need to cut.
- Pick a unit if you'd like it labeled in the output — it's purely cosmetic; rise and run just need to already share the same unit.
The pitch, angle, slope percent, and rafter length multiplier appear instantly, along with a table comparing your pitch to common named roof slopes — from the minimum shingle-safe slope up to a steep 45° chalet roof.
The math
- Pitch (X/12) =
rise ÷ run × 12— normalized to the standard 12-unit run, regardless of what run you actually measured - Angle =
atan(rise ÷ run), converted from radians to degrees - Slope (%) =
rise ÷ run × 100 - Rafter Length Multiplier =
√(rise² + run²) ÷ run— the hypotenuse-to-run ratio. Multiply any horizontal run by this number to get the rafter length needed to span it - Rafter Length (for your run) =
run × Rafter Length Multiplier, i.e.√(rise² + run²)
For example, a standard 6/12 roof (rise 6 over a run of 12) has an angle of about 26.57°, a 50% slope, and a rafter length multiplier of about ×1.118 — so a 12 ft run needs about 13.42 ft of rafter.
What's a "good" roof pitch?
It depends on the roofing material and climate. A few common reference points:
| Pitch | Angle | Notes |
|---|---|---|
| 2/12 | 9.46° | Minimum slope for low-slope/membrane roofing |
| 3/12 | 14.04° | Minimum slope for asphalt shingles |
| 4/12 | 18.43° | Common on ranch-style homes |
| 6/12 | 26.57° | Most common residential pitch — comfortably walkable |
| 9/12 | 36.87° | Steep — common on craftsman and A-frame styles |
| 12/12 | 45° | Very steep, chalet-style |
Does rise and run need to be in feet?
No — any consistent unit works (inches, feet, meters), since the pitch, angle, and slope are all unitless ratios. The unit selector only labels the rafter length in the result table.
For a broader ramp/road/driveway slope tool (ratio, grade %, angle, and slope length from any rise/run), use the Slope Grade Calculator. For a general right-triangle solve, use the Triangle Calculator.
Everything runs in your browser; no inputs are sent to a server.