Depth Of Flow In Pipe Calculator

Calculate pipe diameter or depth of flow in a full pipe using the other value, with results in feet, inches, or meters as needed.

Depth Of Flow In Pipe Formula

Under the full-pipe assumption used by this calculator, the depth of flow is equal to the inside diameter of the pipe. This applies when the circular pipe is flowing full to the crown.

DF = PD

To solve for pipe diameter when depth of flow is known, the same relationship is rearranged as:

PD = DF

For unit conversion, the calculator converts the entered value to feet first, then converts the result to your selected output unit:

Value_ft = Value * Conversion_Factor

DF = depth of flow
PD = pipe diameter
Value_ft = the entered value converted to feet
Conversion_Factor = unit conversion factor to convert the selected unit into feet

If you enter the pipe diameter, the calculator returns the depth of flow using DF = PD. If you enter the depth of flow, it returns the pipe diameter using PD = DF. The calculator requires exactly one of the two fields to be blank so it knows which value to solve for.

Common Pipe Diameters and Full-Flow Depths

For a circular pipe flowing full, the full-flow depth is the same as the pipe diameter.

Pipe Diameter	Equivalent Feet	Depth of Flow When Full
6 in	0.50 ft	6 in
12 in	1.00 ft	12 in
18 in	1.50 ft	18 in
24 in	2.00 ft	24 in
36 in	3.00 ft	36 in

Length Unit Conversions Used

Unit	To Feet	From Feet
Feet	1 ft = 1 ft	1 ft = 1 ft
Inches	1 in = 0.083333 ft	1 ft = 12 in
Meters	1 m = 3.28084 ft	1 ft = 0.3048 m

Example Problems

Example 1: Find depth of flow from pipe diameter

You have a circular pipe with a diameter of 24 inches and want the full-flow depth.

DF = PD

DF = 24 in

The depth of flow is 24 inches, or 2 feet.

Example 2: Find pipe diameter from depth of flow

You know the full-pipe depth of flow is 0.75 meters.

PD = DF

PD = 0.75 m

The pipe diameter is 0.75 meters. In feet, this is about 2.4606 feet.

FAQ

Is depth of flow always equal to pipe diameter?

No. Depth of flow is equal to pipe diameter only when a circular pipe is flowing full. If the pipe is partially full, the depth of flow is less than the pipe diameter.

What does depth of flow mean in a pipe?

Depth of flow is the vertical distance from the lowest inside point of the pipe to the water surface. In a full circular pipe, the water surface reaches the top inside point of the pipe, so the depth equals the inside diameter.

Should I use inside diameter or outside diameter?

Use the inside diameter. Flow depth is measured inside the pipe, so the wall thickness should not be included in the diameter value.