Cyclists will often talk about (or brag about) various hill climbs and gradients they've conquered on their rides. "I just did a 5 mile, 12% climb at Mount so and so".
What exactly is a gradient? Most people think it's an angle like you would see on a protractor. That's not the case, and of course that would be too easy.
In it's simplest terms, gradient refers to the percentage of rise that a roadway has over a predetermined distance - oftentimes referred to as "rise-to-run". For example, if you were to climb 7' in elevation (rise) over a distance of 100' (run), than you've ridden up an incline of 7%.
What makes this formula really handy, is the fact that it works in any language or measurement (meters for example). If you rise 7 meters over a distance of 100 meters, than you've still got that same gradient of 7%. So if you were to cycle the Pyrenees mountains of France or the Rockies of Colorado, a sign stating 7% incline, means the same thing internationally.
So how steep is steep? While riding a bike you might not notice an uphill gradient of 1 or 2%. It's a very small incline. Once you reach a rise of 3-4%, you'll feel it. 5% and you'll be working. 6-8% and you'll be in one of your lower gears just to get over the hill. And climbing grades of 10% or more can be a real struggle. This is just about as steep as you'll find on "normal" roads.
Once you exceed 10%, you're either climbing a mountain or wishing that the road crew could have eliminated this hill during construction. This is where gravity takes over and you're struggling to move forward.
Believe it or not, you may occasionally encounter hills exceeding 20% for short distances. These are common in mountainous areas and foothills surrounding mountains.
In order to know the exact gradient that you're riding, all you need is a cycling computer that calculates the slope you're climbing. There's several on the market and it's fun looking at the percentages as your going (struggling) uphill.
Here is a chart showing gradient (red line) and degrees. For example a 10% grade is equal to an angle of 5.71 degrees. It doesn't look very steep, but on a bike it sure is.
So the next time someone asks you about gradient, tell them you just rode up a steep hill with a 30% gradient. They won't know that it was actually 16.7 degrees.