Gradient and fall calculator
The calculator needs JavaScript. The worked example, formula and figures below show exactly how it works, so you can do the sum yourself. A guide, not advice. Check your supplier's or maker's figures before ordering.
Short answer
Worked example
| You enter | Value |
|---|---|
| What do you know? | The gradient |
| Gradient given as | 1 in n |
| Gradient | 60 |
| Length of the run | 3 m |
| What is it for? | Patio |
1:60 = 1.67% = 0.95° = 16.7 mm per metre; drop 50 mm
| Result | Value |
|---|---|
| As 1 in n | 1:60 |
| As a percentage | 1.67% |
| In degrees | 0.95 ° |
| Millimetres per metre | 16.7 mm/m |
| Drop over the length | 50 mm |
| Where the figure for this use comes from | Patio: the fall comes from the slab maker's laying guide (see the patio calculator). |
Show the working
- 1:60 is a slope of 0.017 (rise per unit of run)
- 1 in n: 1 ÷ 0.017 = 60; percentage: 0.017 × 100 = 1.67%; degrees: arctan(0.017) = 0.95°; mm per metre: 0.017 × 1000 = 16.7
- Drop: 3 m × 0.017 = 50 mm
How it works
- Slope s = rise ÷ run. 1 in n: s = 1 ÷ n. Percentage = s × 100. Degrees = arctan(s). mm per metre = s × 1000
- Drop over a length = length × s
- From a measured drop: s = drop ÷ length
Patio falls come from the slab maker's laying guide, drain gradients from Approved Document H, flat-roof falls from the membrane maker and ramp gradients from Approved Document M: use the linked calculators for those figures.
Our default (adjustable)
These are typical planning figures and our own allowances, not facts about your product. Change any of them in the calculator to match your bag, pack or tin.
This calculator has no built-in defaults: every figure comes from you or your product's data.