# How to Calculate Pipe Length

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#### Things You'll Need

• Calculator

• Physical data for pipe type

#### Tip

Pipe physical data and flow loss data are invaluable for all engineering calculations regarding pipes.

#### Warning

Pressure ratings of piping systems should always be considered before using a pipe line for a highly pressurized system.

There are a number of situations where the length of a pipe must be determined by means other than just measuring it with a ruler or tape measure. One is when the pipe is buried or submerged for much of its length, or otherwise inaccessible. Another might be that the pipe is too long for classic measurement means. It is possible to calculate pipe length by using other related measurements in either of these two scenarios.

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## Step 1

Define the pipe line in question. In this example, a butt-welded 1-inch Schedule 40 steel water pipeline of unknown length is run throughout an industrial facility. If it takes 9.24-gallons of water to completely fill the pipeline from empty, you can calculate pipe length.

## Step 2

Calculate the volume of one foot of 1-inch Schedule 40 steel pipe. Published data shows that the internal diameter is 1.05-inches. Using the volume formula for cylinders, V= (diameter/2)^2 X pi X length X 7.48 gallons/cubic foot. Substituting terms V = (1.05/2) ^squared X 3.1416 X 12 = 0.0449788-gallons/foot of pipe.

## Step 3

Calculate the length of the pipe by dividing its 9.24-gallon internal volume by 0.0449788-gallons/foot of pipe to yield 205.43-feet. Since the pipe is butt-welded from the outside, there are no fittings or intrusions to affect this volume, and the pipe can be considered uniformly smooth on the inside, and the 205.43-foot length accurate.

## Step 1

Define the pipe line in question. Using the same case as Section 1, a butt-welded 1-inch Schedule 40 steel water pipeline of unknown length is run throughout an industrial facility. When a precise 10-gallon-per-minute (gpm) flow is metered through the pipe, the 60-pound-per-square-inch (psi) entry flow drops by 5.91-psi. You can calculate pipe length from this information.

## Step 2

Look up the pressure-loss data for 1-inch Schedule 40 steel pipe. The chart shows that at 9.5-gpm, water loses 2.6-psi per 100-feet of pipe.