A roof pitch calculator turns two measurements, the vertical rise and the horizontal run, into a pitch in degrees, a ratio or millimetres of fall per metre. Most calculators are free, and you only need a tape, a level and a calculator app to get a reliable answer without climbing onto the roof.
This guide shows the roof pitch formula, how to measure safely, the minimum pitch for common roofing materials, and when to call a roofer instead of trusting a number.
Key points
- Pitch is rise divided by run, and the same roof can be written as degrees, a ratio such as 1 in 200, or millimetres of rise per metre.
- Corrugated polycarbonate needs at least 5 degrees, about 88 mm of fall per lineal metre, or water sits at the laps and leaks.
- Every roofing material has its own minimum pitch, so check the manufacturer’s data sheet before you choose a roof or a patio design.
- Measure from inside the roof space, the ground or a ladder at the eave, and never walk on a roof just to take a reading.
What is a roof pitch calculator?
A roof pitch calculator is a tool that does the trigonometry for you, so you do not need to remember the formula on site. You enter two numbers and it shows the roof pitch in the format your supplier or builder asks for.
| Term | What it means | Why it matters |
|---|---|---|
| Roof pitch | The slope of a roof, shown as degrees, a ratio or a percentage | Decides which roofing materials and profiles are allowed |
| Rise | The vertical height the roof gains over the run | The first number a roof pitch calculator needs |
| Run | The horizontal distance covered by the slope | Measure it level, not along the slope |
| Fall | The drop from the high edge to the low edge of the roof | Used for flat roofs, gutters and patios, often as a ratio such as 1 in 200 |
| Skillion | A single-slope roof with no ridge | Often built at low pitch, so the minimum matters |
- Input one: the rise, measured in millimetres between the high and low points of the slope.
- Input two: the run, measured level between the same two points, in the same units.
- Output: the angle in degrees, a ratio such as 1 in 200, a percentage or mm of rise per metre.
Types of roof pitch calculator
You can use an online roof pitch calculator, a phone app or a spirit level and tape, and they all give the same answer if you measure carefully.
| Type | Best for | Accuracy / limits | Cost |
|---|---|---|---|
| Online roof calculator pitch tool | Quick answers from rise and run | Only as good as your measurements | Free |
| Omni roof pitch calculator | Switching between degrees, ratio and percent | Great for converting formats, no site measuring | Free |
| Phone app or digital level | Reading the angle off a rafter or sheet | Check the calibration on a known flat surface | Free to low cost (indicative — get itemised quotes) |
| Spirit level, tape and formula | Patios, carports and skillions on site | Reliable when both measurements are level and straight | Under a few dollars (indicative — get itemised quotes) |
| Roofer’s inspection | Complex roofs and compliance questions | Includes structure, materials and drainage checks | Often free with a quote (indicative — get itemised quotes) |
- Roof pitch calc apps: good for a quick check, but never rely on a single reading when you are ordering sheets or trusses.
- Roof fall calculator: the same maths applied to a flat roof or patio, usually shown as mm per metre.
- Roof pitch degree calculator: converts a ratio such as 1 in 200 to an angle in degrees.
How to calculate roof pitch
Divide the rise by the run to get the slope, then convert it to the format you need.
- Measure the rise as the vertical height between the low point and the high point of the slope, in millimetres.
- Measure the run as the level distance between those same two points, in millimetres.
- Divide rise by run to get the slope as a decimal, for example 0.0875 for a slope that gains 87.5 mm in a metre (indicative — worked example only).
- Multiply by 1000 to get millimetres of rise per metre, which is how many suppliers publish minimum fall.
- Find the angle by taking the inverse tangent of the slope on a calculator or in a roof pitch calculator.
- Write down the result in degrees and in mm per metre, so you can match it to any data sheet.
Roof pitch formula: rise per metre run
This table converts common pitches into rise per metre run, using the roof pitch formula above (indicative — calculated values, confirm on site).
| Pitch (degrees) | Rise per metre run | Typical use |
|---|---|---|
| 2 degrees | About 35 mm (indicative — calculated value) | Low-pitch long-run metal roofs, if the profile allows |
| 5 degrees | About 88 mm | Minimum for corrugated polycarbonate sheeting |
| 10 degrees | About 176 mm (indicative — calculated value) | Skillions, carports and lean-tos |
| 15 degrees | About 268 mm (indicative — calculated value) | Many tile roofs begin here, but check the tile data sheet |
| 22 degrees (indicative — example pitch) | About 404 mm (indicative — calculated value) | Common project-home gable pitch |
| 30 degrees (indicative — example pitch) | About 577 mm (indicative — calculated value) | Steeper gables, with extra care for access |
How to measure roof pitch safely
- Choose the safest spot: measure from the roof space, the carport edge or a ladder at the eave, and never from the roof itself.
- Use a level and tape: hold a straight board level against the rafter, then measure the vertical gap between the board and the rafter.
- Read the angle with an app: place the phone flat on a rafter or sheet, calibrate it first and take three readings.
- Measure from the ground: photograph the gable end square-on and measure the angle in the image if you can’t get near the roof.
- Check against the plans: compare your result with the building plans, which often list the roof pitch.
- Call a roofer if unsure: a licensed roofer has the edge protection and ladders to measure safely.
Minimum roof pitch: corrugated iron, polycarbonate and Queensland
| Roof type | Minimum pitch | What to check |
|---|---|---|
| Corrugated polycarbonate sheet | 5 degrees, about 88 mm per metre | End lap, purlin spacing and fixings from the Laserlite data |
| Corrugated iron minimum fall | Depends on the profile and lap (indicative — check the manufacturer’s data sheet) | Longer sheets and sealed laps allow lower pitch |
| Concrete or terracotta tiles | Often around 15 degrees (indicative — check the manufacturer’s data sheet) | Lower pitch needs sarking and special detailing |
| Minimum roof pitch in Queensland | Set by the product and wind region (indicative — check the manufacturer’s data sheet) | Cyclone-rated fixings may apply |
| Flat roof or box gutter | Falls often written as 1 in 200 (indicative — check the membrane data sheet) | Needs drains sized for storms |
- Pitch isn’t just angle: sheet length, lap type and sealant also affect whether low pitches stay watertight.
- Polycarbonate check: end laps are 150 mm on steeper pitches and 200 mm on shallow pitches, and gutter overhang is 50 mm.
- Warranty: installing below the minimum pitch can void the warranty, so confirm before ordering materials.
Skillion roof pitch and pitched roof patio
- Skillion roof pitch: check the roofing profile first, because a skillion often sits near the minimum, and see our skillion roof guide.
- Pitched roof patio: a patio roof attached to the house needs fall away from the wall so water never pools at the flashing.
- Rafter span: a lower pitch can still need strong rafters; our truss and rafter span guide covers spans.
- Lining: raked skillion ceilings can use the ideas in our internal wall cladding ideas.
- Insulation: a skillion has little roof space, so see our roof insulation guide for options.
- Colour: a long, low roof is highly visible; the Lexicon Quarter vs Half vs Full guide helps you choose a trim shade.
Flat roof pitch calculator and 1 in 200 fall
- Fall ratio: a flat roof pitch calculator expresses fall as a ratio, and 1 in 200 means 1 unit of fall for every 200 units of run.
- In millimetres: 1 in 200 is about 5 mm of fall per metre, so a 4 m run drops about 20 mm (indicative — calculated value).
- Not truly flat: flat roofs still need fall to drain, and ponding water shortens the life of any membrane.
- Box gutters: a pitched roof box gutter detail needs fall to the downpipe, an overflow and a sump sized to the catchment.
- Waterproofing: low-fall roofs rely on the membrane, so choose a product made for low fall and follow its data sheet.
- Drainage: check downpipes and overflows before every storm season, because blocked outlets flood low-fall roofs quickly.
Pitched roof vs gable roof: what changes
| Roof | Pitch behaviour | Best for |
|---|---|---|
| Pitched roof | Any sloped roof; the umbrella term | Most Australian homes |
| Gable roof | Two planes meeting at a ridge, with triangular end walls | Easy water shedding, simple framing |
| Hip roof | Slopes on all four sides | Wind resistance and a neat eave line |
| Skillion roof | One plane, usually lower pitch | Modern homes and extensions |
| Flat roof | Minimal fall, hidden behind parapets | Terraces and modern architecture |
For more shapes and how each performs in Sydney weather, see our guide to roof types in Australia.
Roof pitch calculator cost: free tools versus a roofer
| Option | Typical cost (AUD, Oct 2026) | When to use it |
|---|---|---|
| Online roof pitch calculator | Free | Quick checks from your own measurements |
| Digital angle finder or inclinometer | $20–$80 (indicative — get itemised quotes) | Frequent measuring on patios and carports |
| Roofer’s measure and quote | Often free for Sydney work (indicative — get itemised quotes) | Compliance, ordering sheets and complex roofs |
| Surveyor or engineer | Several hundred dollars (indicative — get itemised quotes) | Structural or legal disputes |
Roof pitch calculator pros and cons
| Pros | Cons |
|---|---|
| Fast and free, with no site visit needed | Garbage in, garbage out if measurements are rough |
| Converts degrees, ratio and percent instantly | Doesn’t check structure, drainage or materials |
| Helps you compare supplier data sheets | Doesn’t replace local rules or an engineer |
| Works for patios, carports and flat roofs | Phone apps drift if not calibrated |
| Lets you check a quote before you sign | Easy to measure along the slope by mistake |
How to choose a roof pitch calculator
- Pick the format you need: degrees for tile and metal data sheets, mm per metre for polycarbonate, ratio for flat roofs.
- Use two tools: check one reading with a level and tape, and another with an app or online calculator.
- Check the units: confirm the roof pitch calculator expects millimetres, metres or inches before you type.
- Test on a known slope: try it on a ramp or a ladder angle before trusting it on your roof.
- Keep your numbers: save the rise, run and result with a photo, so your roofer can see how you got there.
- Know when to stop: if the result is near a minimum, ask a roofer to confirm on site.
Using your roof pitch calculator result on site
- Compare to the data sheet for your sheet or tile and confirm the pitch is above the minimum.
- Check polycarbonate spans if you are building a patio: corrugated allows 800 mm end and 1000 mm mid span between purlins.
- Allow for lap length: choose full-length sheets where possible so end laps don’t sit on the flattest part of the roof.
- Add fall for gutters, and keep the 50 mm overhang into the gutter that the Laserlite data specifies.
- Recheck after framing: measure again once the frame is built, because small errors add up across a long run.
- Plan a clear polycarbonate roof using our polycarbonate roofing guide for fixings and colours.
Roof pitch calculator FAQs
How to calculate roof pitch?
Measure the rise and the run in the same units, divide rise by run, then convert the result to degrees, a ratio or millimetres per metre. A roof pitch calculator does this in seconds. Always measure the run level rather than along the slope, or the answer will be wrong.
How to work out pitch of roof from the ground?
Photograph the gable end square-on from a distance, then measure the angle of the roof edge against a horizontal line in the image. This gives a good estimate. For ordering materials, confirm it with a level and tape from the roof space or eave.
How to measure roof pitch without climbing on the roof?
Use the roof space: hold a level against a rafter and measure the vertical gap over a set length. You can also use a phone angle app on a rafter, or measure at the eave from a ladder. Never walk on the roof just to take a reading.
How to work out the pitch of a roof for a patio?
Measure the height difference between the house end and the low end, then divide by the length of the patio. For corrugated polycarbonate you need at least 5 degrees, about 88 mm of fall per metre, so check the result against that figure.
What is a 5 degree roof pitch per metre?
A 5 degree pitch is about 88 mm of rise per metre of run. It is the minimum for corrugated polycarbonate sheeting and a useful reference point when you set the fall on a patio, carport or lean-to frame.
Is a 2 degree roof pitch enough?
Only some metal profiles with long unbroken sheets and sealed laps are made for a 2 degree roof pitch, and polycarbonate isn’t one of them. Check the manufacturer’s data sheet for your product, and ask a roofer to confirm the detail on site.
Getting roof pitch calculator results checked in Sydney
A roof pitch calculator gives you a number, but a licensed roofer tells you whether the roof will actually stay dry. TQN Construct’s roofers measure your pitch on site, check it against the sheeting data and quote the right profile, fixings and flashings. Book a free measure and quote.
