Slope percentage — quick, practical guide
Core idea
Slope % tells how steep something is: the rise compared to the horizontal run, expressed as a percentage.
How it works
Formula: (Rise ÷ Run) × 100%
- Angle link: slope% = tan(θ) × 100
- Ratio link: 1 : (100 ÷ slope%)
Sanity checks
- Run must be > 0
- 45° slope → 100%
- ADA ramps ≈ 8.33% (1:12)
Shortcuts
- Angle (deg) ≈ arctan(slope% ÷ 100)
- Roof pitch: rise/run as “x/12”; convert to % with (x ÷ 12) × 100
Pitfalls
- Mixing units for rise/run (keep them consistent)
- Confusing grade (%) with angle (degrees)
- Very small run inflates % and error
Micro‑examples
- Rise 3, Run 12 → (3/12)×100 = 25%
- Angle 14.04° → tan(14.04°)×100 ≈ 25%
- Pitch 6/12 → (6/12)×100 = 50%
Mini‑FAQ
% vs ratio? 25% equals 1:4 (1 up for 4 across).
Negative slope? Use a negative rise to indicate downhill; magnitude is the same.
Action tip
For designs, include angle°, %, and ratio forms together to avoid ambiguity across teams.