How to Calculate Flow Rate With Pipe Size and Pressure

Water pressure drives a pipe's flow.
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A higher pressure drop acting on a pipe creates a higher flow rate. A wider pipe also produces a higher volumetric flow, and a shorter pipe lets a similar pressure drop provide a greater force. The final factor controlling a pipe's viscosity is the fluid's viscosity. This factor measures the fluid's thickness in poise, or dyne seconds per square centimeter. A thicker fluid flows more slowly under the same pressure.

    Square the pipe's radius. With a radius, for instance, of 0.05 meters, 0.05 ^ 2 = 0.0025.

    Multiply this answer by the pressure drop across the pipe, measured in pascals. With a pressure drop, for instance, of 80,000 pascals, 0.0025 x 80,000 = 200.

    Multiply the constant pi by the answer to Step 1: 3.142 x 0.0025 = 0.00785. This answer is the pipe's cross-sectional area.

    Multiply the area by the answer to Step 2: 0.00785 x 200 = 1.57.

    Multiply the pipe's length by 8. With a length, for instance, of 30 meters: 30 x 8 = 240.

    Multiply the answer to Step 5 by the fluid's viscosity. If the fluid is water, its viscosity is 0.01, so 240 x 0.01 = 2.4.

    Divide the answer to Step 4 by the answer to Step 6: 1.57 / 2.4 = 0.654. The pipe's flow rate is 0.654 cubic meters per second.