Slope & fall
Skip the mental arithmetic. Enter the length and the fall, and the height difference comes straight back – plus the slope in both percent and as a ratio (1:X). Handy for drainage, ground and roofs, where fall is often given in different ways.
Slope & fall – work out the height difference
Enter the length and the fall in mm per metre and we work out the total height difference, the slope in percent and as a ratio (1:X). Handy for drainage, ground and roofs.
Guide values: drain pipes often 10–20 mm/m, ground away from the foundation at least 15 mm/m (1:50) for the first few metres, fall to a floor drain in a shower 1:150 (7 mm/m) to 1:50 (20 mm/m). Follow the applicable industry rules for your application.
This tool gives an estimate and is an aid – not a finished calculation. Always check the result against drawings, applicable regulations, supplier data and your professional experience before giving a binding price, ordering material or using the file. ByggExp is not responsible for decisions made solely on the basis of the tool.
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How to work out the fall
- Enter the length in metres.
- Enter the desired fall in mm per metre.
- See the height difference, the slope in percent and as 1:X.
Guide values
The fall you need depends on the application and is usually set out in a drawing or industry rule. The same value can be given as mm per metre, percent or ratio (1:X) – the calculator converts between all three, so you can match the requirement without doing the maths by hand.
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Frequently asked questions
- How do I work out the fall?
- Fall is often given in mm per metre. The height difference is the length times the fall: 6 m at 15 mm/m gives 90 mm. The calculator also shows percent and ratio.
- What fall should the drain have?
- Guide values are often 10–20 mm per metre for drain pipes, but it depends on pipe dimension and application. Follow the applicable industry rules.
- How much fall away from the foundation?
- The ground should slope away from the house, often at least 15 mm per metre (1:50) for the first few metres, to drain water away.
- Does it cost anything?
- No, the calculator is free and requires no account.