Drainage Slope Calculator
Enter the drainage length and slope percentage to compute the fall (mm) and slope ratio (1:N), and check against Hong Kong's common minimum 1:80 (≈1.25%) requirement.
輸入資料
計算結果
重點速覽：Drainage slope is given as a percentage: units dropped per 100 horizontal units. Fall = length(m) × slope% × 10 (to mm). Slope ratio = 1 : (100 ÷ slope%). In Hong Kong, waterproofed indoor floors (bathrooms, kitchens) commonly need a fall no less than 1:80, i.e. ≈1.25%; too flat ponds water, too steep is awkward to build and use.
計算公式
Fall (mm) = length (m) × slope% × 10
Slope ratio = 1 : (100 ÷ slope%)
Compliant if slope% ≥ 1.25
$$f = L\times p\times 10$$$$R = 1 : \frac{100}{p}$$$$p \ge 1.25\%$$使用說明
- Enter the horizontal drainage length (m).
- Enter the slope percentage (Hong Kong floors commonly 1–2%).
- The tool outputs fall, slope ratio and a drainage compliance check.
理財情境案例
Bathroom floor
Length 3 m, slope 1.5%.
Fall 45 mm, ratio 1:67, compliant with the ≥1.25% requirement.
Balcony drainage
Length 5 m, slope 1%.
Fall 50 mm, ratio 1:100, below 1.25% — increase the slope.
常見問題
What is a 1:80 slope?
It means 1 unit drops per 80 horizontal units, i.e. 1/80 = 1.25%. Hong Kong waterproofed floors commonly use this as the minimum.
Is steeper always better?
No. Too steep makes the floor visibly tilted and awkward to walk and place items, and harder to tile; 1–2% is usually best.
相關工具
參考資料
Content reviewed by the Hong Kong Calculator construction team. Floor fall and slope-ratio calculation verified against Hong Kong's common waterproofed-floor drainage design rule (no less than 1:80).