Slope & Grade Calculator
Percent, ratio (1 in N), degrees and total fall from rise and run — plus a drainage mode for pipe fall per foot, with the math shown.
Your slope
Slope
2.083%
- Ratio
- 1 in 48
- Angle
- 1.193°
- Total fall
- 12 in (1 ft)
How this is calculated
Slope percent
rise ÷ run × 100
= 1 ÷ 48 × 100
2.083%
Angle
atan(rise ÷ run) × 180 ÷ π
= atan(1 ÷ 48) × 180 ÷ π
1.193°
Ratio
run ÷ rise (1 in N)
= 48 ÷ 1
1 in 48
How to calculate slope, grade and fall
Slope is rise over run. A 1 ft rise over a 48 ft run is 1 ÷ 48 × 100 = 2.083%, a ratio of 1 in 48, and an angle of atan(1 ÷ 48) = 1.19°. For drainage, multiply the pipe length by the required fall per foot — 50 ft at 1/4 in per ft is 12.5 in of total fall.
Slope: percent, ratio and degrees
| Percent | Ratio (1 in N) | Angle | Fall per ft |
|---|---|---|---|
| 1% | 1 in 100 | 0.57° | 0.12 in |
| 2.083% | 1 in 48 | 1.19° | 0.25 in |
| 1.042% | 1 in 96 | 0.60° | 0.125 in |
| 5% | 1 in 20 | 2.86° | 0.60 in |
| 25% | 1 in 4 | 14.04° | 3.00 in |
| 100% | 1 in 1 | 45.00° | 12.00 in |
Common minimum drainage slopes (guidance only)
| Pipe size | Minimum fall per ft | Slope |
|---|---|---|
| 2½ in and smaller | 1/4 in | 2.08% |
| 3 in to 6 in | 1/8 in | 1.04% |
| 8 in and larger | 1/16 in | 0.52% |
Plumbing tools
Common slope mistakes
- •Confusing percent with degrees. A 2% slope is only 1.15° — they are not interchangeable. This tool shows both.
- •Too much drainage fall. Over-steep drains let water outrun solids and cause blockages — meet the minimum, do not far exceed it.
- •Treating code minimums as exact. They vary by jurisdiction and pipe type — always verify against your local plumbing code.
Frequently asked questions
How do I calculate slope percentage?+
Slope percent = rise ÷ run × 100. A 1 ft rise over a 48 ft run is 1 ÷ 48 × 100 = 2.083%.
How do I convert slope to degrees?+
Angle = atan(rise ÷ run) × 180 ÷ π. A 1 in 48 slope is atan(1 ÷ 48) = 1.19°. A 2% slope is about 1.15°, not 2°.
What is the minimum slope for a drain pipe?+
Common minimums are 1/4 inch per foot (2.08%) for pipes 2½ inches and smaller, and 1/8 inch per foot (1.04%) for 3 to 6 inch pipe. These are guidance only — verify against the plumbing code in force where you work.
How do I calculate pipe fall?+
Total fall = pipe length × fall per foot. A 50 ft run at 1/4 inch per foot drops 12.5 inches end to end.
Methodology & sources
Slope percent = rise ÷ run × 100. Angle = atan(rise ÷ run) × 180 ÷ π, carrying full precision. The ratio is expressed as 1 in N where N = run ÷ rise. Drainage fall = pipe length × fall per foot.
Drainage minimums shown are common code-style guidance only. Required slopes vary by jurisdiction and pipe type — always verify against the plumbing code in force where you work.
Last reviewed June 28, 2026. Estimates are indicative — verify against current product specs and local requirements before ordering.
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