# Slope & Grade Calculator — Percent, Degrees, Ratio & Fall > Free slope and grade calculator: convert between grade percent, angle in degrees, 1:N ratio and rise per run live, and turn any run, rise or slope length into the other two plus the total fall — for drainage, roofs, ramps and grading, all in your browser. Convert grade percent, angle, 1:N ratio and rise per run live — then work out run, rise, slope length and total fall over any distance. - **HTML page:** https://siteometry.com/en/tools/slope-grade-calculator - **Category:** [Earthworks & Excavation](https://siteometry.com/en/tools/category/earthworks-excavation) - **Figures live on the page:** tables, diagrams and worked figures the text refers to ("the table below") are drawn by the page and are not reproduced here. Each section below links to its anchor on the page. - **Runs in the browser:** Siteometry calculators need no account and send no input anywhere — every number below is computed on the visitor's own device. ## How to convert and measure a slope in 4 steps 1. **Enter what you know** — Type a grade percent, angle, 1:N ratio or rise per run into any field. The other three fill in immediately from the same underlying slope. 2. **Choose your units** — Use the Units control to switch between imperial (inches per foot, feet) and metric (millimetres per metre, metres). The choice is remembered on your device. 3. **Add a distance (optional)** — In the distance block choose whether you measured the run, the rise or the slope length, enter it, and read the other two lengths plus the total fall. 4. **Read and share the results** — The table shows every representation at once. Copy a row or the whole table, export a CSV, print a sheet, or copy a link that reproduces the exact slope and distance. _On the page: https://siteometry.com/en/tools/slope-grade-calculator#howto_ ## Slope and grade calculator Slope is a single idea written four different ways. A road engineer calls it a grade percent, a carpenter reads it as an angle in degrees, a civil drawing gives it as a 1:N ratio, and a drainlayer sets it in inches of fall per foot of run. They all describe the same rise over the same run — but a number in one notation means nothing until you can read it in the others. This calculator keeps every notation in step. Type a grade, an angle, a ratio or a rise-per-run figure into any field and the rest update instantly, all derived from one exact slope so they never disagree. Add a measured run, rise or slope length and it works out the other two lengths plus the total fall over that distance. Everything runs in your browser — nothing you type is uploaded, and there is no account to create. It is drainage-first but covers roof pitch, ramp grades, driveway slopes and cut-and-fill batters just as well. _On the page: https://siteometry.com/en/tools/slope-grade-calculator#slope-intro_ ## How to use the slope calculator Start with whatever you already know. If a plan gives you a 2% grade, type 2 into the Grade field; if a drawing shows 1:40, type 40 into the ratio; if you measured 4.76° with a level, type that into the Angle field. Every other representation, the diagram and the results table update from that one value. To find a fall over a real distance, choose what you measured in the distance block — run, rise or slope length — enter it, and read the other two lengths and the total fall below. Switch between imperial and metric with the Units control: imperial expresses rise-per-run as inches per foot and lengths in feet, metric uses millimetres per metre and metres. _On the page: https://siteometry.com/en/tools/slope-grade-calculator#how-it-works_ ## Reading a slope: rise, run and angle Every slope is a right triangle. The run is the horizontal distance, the rise is the vertical distance it climbs or falls over that run, and the slope length is the hypotenuse — the distance actually travelled along the surface. The angle sits between the run and the slope length. Grade percent is simply rise ÷ run × 100, so a 1-foot rise over a 100-foot run is a 1% grade. A 1:N ratio is the same relationship inverted: 1 unit of rise for every N units of run, so 1:100 is also 1%. Because the slope length is always a little longer than the run, this tool also reports a slope-length multiplier (√(1 + slope²)) — multiply the run by it to get the true surface length, which matters for measuring roof sheeting or ramp handrails. _On the page: https://siteometry.com/en/tools/slope-grade-calculator#reading-a-slope_ ## Grade, angle, ratio and per run The four notations convert cleanly. Grade percent and the 1:N ratio are two views of the same fraction; the angle is its arctangent; and rise per run is the grade scaled to a standard length of run — 12 inches in imperial, 1000 millimetres in metric. The table below the input shows all of them at once for whatever slope you enter, plus per mille (parts per thousand), the notation many European drainage standards use. One point of confusion is worth flagging: the roofing '1:N' written as 'x-in-12' (for example 4-in-12 pitch) is not the same as the civil-drainage 1:N ratio. A 4-in-12 roof is a 1:3 ratio and a 33% grade, not 1:4. For roof pitch specifically, use the rafter length calculator, which is built around the x-in-12 convention. _On the page: https://siteometry.com/en/tools/slope-grade-calculator#conversion-reference_ ## Drainage and ramp slopes For surface and pipe drainage, trades commonly aim for a minimum fall so water keeps moving without the flow going too slow to carry solids. A rule of thumb for small pipes is ¼ inch per foot (about 1:48, or 2%), with ⅛ inch per foot (about 1:96, or 1%) used on longer runs or larger pipes. These are conventions, not universal law — the governing plumbing or drainage code and the pipe size set the real minimum, so verify locally. For accessible ramps, the widely cited maximum running slope is 1:12 — an 8.33% grade, about 4.76° — with gentler slopes preferred and cross slope limited separately. Treat 1:12 as the ceiling for new work and confirm the requirement that applies to your project. This calculator makes both easy to check: tap a preset or type the ratio and read the fall over your actual run in the distance block. _On the page: https://siteometry.com/en/tools/slope-grade-calculator#drainage-and-ramps_ ## Frequently asked questions ### How do I convert a grade percentage to degrees? Take the arctangent of the grade written as a fraction: angle = arctan(percent ÷ 100). A 10% grade is arctan(0.10) ≈ 5.71°, and an 8.33% grade is about 4.76°. Type the percentage into the Grade field and the calculator shows the angle, ratio and rise per run instantly. ### What is the difference between grade percent and a 1:N ratio? They are the same slope written two ways. Grade percent is rise ÷ run × 100; a 1:N ratio is 1 unit of rise for every N units of run. So 1:100 is 1%, 1:50 is 2%, and 1:12 is about 8.33%. To convert a ratio to a percentage, divide 100 by N. ### Is a 1:N ratio the same as roof pitch (x-in-12)? No. Roof pitch is written as rise-in-12 — for example 4-in-12 — which is 4 units of rise for every 12 of run, a 1:3 ratio and a 33% grade, not 1:4. The civil 1:N ratio uses 1 unit of rise for N of run. For roof pitch specifically, use the rafter length calculator, which is built around the x-in-12 convention. ### What slope do I need for drainage? A common rule of thumb for small pipes is ¼ inch of fall per foot of run — about 1:48 or 2% — with ⅛ inch per foot (roughly 1:96 or 1%) used on longer runs and larger pipes. These are trade conventions; the governing plumbing or drainage code and the pipe diameter set the real minimum, so always verify locally. ### What is the maximum slope for a wheelchair ramp? The widely cited maximum running slope for an accessible ramp is 1:12 — an 8.33% grade, about 4.76° — with gentler slopes preferred where space allows. Treat 1:12 as a ceiling for new work and confirm the exact requirement that applies to your project, since cross slope and landing rules apply separately. ### How do I work out the total fall over a distance? Set the slope, then use the distance block: choose whether you measured the run, the rise or the slope length, enter it, and the calculator returns the other two lengths and the total fall. For example, a 2% grade over a 10-foot run gives a fall of about 0.2 ft (roughly 2½ inches). ### Why does a flat slope show no ratio? A ratio of 1:N means 1 unit of rise for every N of run. A perfectly flat slope has zero rise, so N would be infinite — there is no meaningful ratio. The calculator shows '— (flat)' instead of a number, while the percent, angle and fall all read zero. ### What is the slope-length multiplier? The slope length (the hypotenuse) is always a little longer than the horizontal run. The multiplier is √(1 + slope²): multiply the run by it to get the true surface length. On a gentle 2% grade it is about 1.0002, so it barely matters; on a steep 33% bank it is about 1.054, adding over 5% to the length you measure or buy. ### Is the calculator private? Yes. Every calculation runs entirely in your browser. Nothing you enter is sent to any server, and only your preferred unit system is remembered, in your own browser's local storage. _On the page: https://siteometry.com/en/tools/slope-grade-calculator#faq_ ## Related calculators - [Rafter Length Calculator](https://siteometry.com/en/tools/rafter-length-calculator) - [French Drain & Drainage Calculator](https://siteometry.com/en/tools/french-drain-calculator) - [Feet & Inches Calculator — Add, Subtract & Convert](https://siteometry.com/en/tools/feet-inches-calculator) - [Roof Pitch Calculator — Slope to Degrees, Percent & X-in-12](https://siteometry.com/en/tools/roof-pitch-calculator)