The British system makes x = 1, ie 1 in 7, which would be a fairly steep road. Find how much crushed stone is needed for a gravel driveway in cubic yards and tons, and estimate the cost of materials. grade = (396 ÷ 15,840) * 100 = 2.5% Stating a ratio such as 1 in 20 tells you immediately that for every 20 horizontal units traveled, your altitude increases 1 unit. The third row shows the calculation of the true horizontal run which is 15840 feet. This chart covers a wider range: Answers are displayed in scientific notation with the number of Let's suppose we are entering a grade that was computed by rise over slope length.   5.2408%, 3) If we know the grade of a road (for example 3%), then Stating this as a percentage, whatever horizontal distance you travel, your altitude increases by 5% of that distance.   (1 ÷ 19.081) * 100 =   1 in 19.081 and the, grade = (rise ÷ run) * 100 which equals Run Length = 500 mm Rise Length = 1200 mm Gradient = 500/ 1200 Gradient = 1:0.4166 Grade measurements are often used in projects ranging from roofing to road construction.