Plumbing & Fluid

Drainage Slope Calculator

Check a drainage gradient from horizontal run and vertical fall, or solve the missing distance or end elevation. The result shows equivalent slope units and the true sloped length.

Change any input to update the calculation. Unit changes preserve the physical quantity.

CALCULATION SETUP

Inputs

Calculated locally in your browser. No sign-up or input upload.

YOUR CALCULATION

Results

Slope

2 %

Gradient ratio

50 (1:X)

Fall per metre

20 mm/m

Fall per metre

2 cm/m

Fall per foot

0.24 in/ft

Slope angle

1.146 °

Vertical fall

0.2 m200 mm7.874 in

Horizontal run

10 m32.808 ft

Sloped length

10.002 m32.815 ft

Ending elevation

99.8 m327.428 ft
Run 10 mFall 0.2 m2% · downhill
Horizontal run, vertical fall and drainage direction · schematic, not to scale

Calculation breakdown

Gradient
1:50 downhill

Assumptions & checks

This is a geometry calculation. Required drainage slopes depend on application, pipe size and local rules; no preset establishes plumbing-code compliance.

Formula

Positive fall means the ending elevation is lower. Run is horizontal, not measured along the pipe.

slope% = 100×fall/run; fall = run×slope%/100; run = 100×fall/slope%; end = start−fall; length = √(run²+fall²); angle = atan(fall/run)

Worked example

Using the default values shown in the calculator, the same formula gives the following result. This is a quick sanity check for the calculation, not a design recommendation.

Inputs

Horizontal run
10 m
Vertical fall
0.2 m
Starting elevation
100 m

Result

Slope
2 %
Gradient ratio
50 (1:X)
Fall per metre
20 mm/m
Fall per metre
2 cm/m
Fall per foot
0.24 in/ft
Slope angle
1.146 °
Vertical fall
0.2 m
Horizontal run
10 m
Sloped length
10.002 m
Ending elevation
99.8 m

Related calculators

Continue your workflow with a related calculation.

View all Plumbing & Fluid calculators

Plumbing & Fluid

Pipe Diameter Calculator

Solve pipe inside diameter, flow or mean velocity from Q = A × v. Convert L/s, L/min, m³/h, US GPM, CFM and metric or imperial pipe dimensions.

Construction

Paver Calculator

Estimate paver pieces with joints and waste, gravel base, bedding sand and edging length. Plan the complete layer stack in metric or imperial units.

Construction

Gravel Calculator

Estimate gravel volume, tonnes, US tons, bags and loads with editable density, waste and compaction. Calculate coverage from a known quantity.

Plumbing & Fluid

Hazen-Williams Calculator

Solve water-pipe friction head loss, pressure loss, flow or inside diameter using Hazen-Williams with editable C-factor and metric or imperial units.

Plumbing & Fluid

Pump TDH Calculator

Estimate pump total dynamic head, pipe and fitting losses, pressure head and hydraulic power with editable fluid properties and metric or imperial units.

Frequently asked questions

Is 2% the same as 2 degrees?

No. Percent is fall divided by horizontal run, multiplied by 100. The angle is the arctangent of fall divided by run; 2% is about 1.146 degrees.

What does 1:X mean?

For a nonzero slope, X is horizontal run per unit of vertical fall. A 2% downward slope is 1:50. Zero is level, and a negative slope is labelled as uphill.