A gradient is a complicated word for quite a simple concept. The gradient refers to the change rate of a slope. Take for instance a gradient of slope that is 1 in 40 (1:40).
A 1:40 slope means that for every 40 metres along the ground, the slope height increases by 1 metre. A 1:0.5 slope means that for every 1 metre along the ground, the slope height increases by 0.5 metres.
A gradient can be expressed in 2 ways, a number or a ratio.
For instance, a 1:40 gradient number is shown as 0.025 (an example is shown in the calculation section).
The same number can be converted into a ratio
For instance, a ratio is shown as “1:40”
The following sketch should help.