Calculate channel slope, height, or length from any two values, converting between in, ft, cm, and m units, with calculation steps.
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Channel Slope Formula
The channel slope is the vertical change in height divided by the horizontal channel length. The calculator uses the same base relationship to solve for slope, height, or length.
S = H / L
H = S * L
L = H / S
- S = channel slope, unitless
- H = channel height, rise, or vertical drop
- L = channel length, run, or horizontal distance
The calculator converts height and length to meters before calculating, so you can enter the two distance values in different units. The final height or length is converted back to the unit selected for that field.
- To calculate channel slope: enter channel height and channel length. The calculator divides height by length.
- To calculate channel height: enter channel slope and channel length. The calculator multiplies slope by length.
- To calculate channel length: enter channel height and channel slope. The calculator divides height by slope.
Common Channel Slope Conversions
A slope is unitless, but it is often shown as a decimal, percent, or ratio. Use the table to interpret the result.
| Decimal Slope | Percent Grade | Approximate Ratio |
|---|---|---|
| 0.001 | 0.1% | 1 in 1000 |
| 0.005 | 0.5% | 1 in 200 |
| 0.010 | 1.0% | 1 in 100 |
| 0.020 | 2.0% | 1 in 50 |
| 0.050 | 5.0% | 1 in 20 |
Length Unit Conversion Factors
The calculator converts distance values to meters internally before applying the slope formula.
| Unit | Meters per Unit |
|---|---|
| inch, in | 0.0254 |
| foot, ft | 0.3048 |
| centimeter, cm | 0.01 |
| meter, m | 1 |
Example Calculations
Example 1: Calculate channel slope
You have a channel height of 0.5 ft and a channel length of 25 ft.
S = H / L = 0.5 / 25 = 0.02
The channel slope is 0.02, which is the same as a 2% grade.
Example 2: Calculate channel height
You have a channel slope of 0.015 and a channel length of 40 m.
H = S * L = 0.015 * 40 = 0.6 m
The channel height is 0.6 m.
FAQ
Is channel slope the same as percent grade?
Channel slope as a decimal is not the same number as percent grade, but they describe the same steepness. To convert decimal slope to percent grade, multiply by 100. For example, a slope of 0.02 equals 2%.
Does height mean rise or drop?
Height means the vertical change between the start and end of the channel. It can be a rise or a drop depending on direction. For drainage or open-channel flow, it is often treated as the vertical drop over the channel length.
Why is channel slope unitless?
Channel slope is unitless because it is a distance divided by a distance. The units cancel out as long as height and length are converted to the same unit before division.
