FPS to GPM Calculator – Feet Per Second to GPM Flow Rate Conversion

The fps to gpm calculator (feet per second to gallons per minute) is designed to convert water flow rates between different measurement units.

When you have a pipe with water flowing at 2.5 feet per second, and you need to know the flow rate in gallons per minute. Using the fps to gpm converter for a 4-inch diameter pipe:

pipe_diameter = 4 inches
flow_velocity = 2.5 fps
calculated_gpm = 97.34 GPM

FPS to GPM Calculator

FPS (Feet per Second)	GPM (Gallons per Minute)
0.5	1.02
1	2.04
1.5	3.06
2	4.08
2.5	5.10
3	6.12
3.5	7.14
4	8.16
4.5	9.18
5	10.20
10	20.40
20	40.80
30	61.20
40	81.60
50	102.00
60	122.40
70	142.80
80	163.20
90	183.60
100	204.00
200	408.00
300	612.00
400	816.00
500	1020.00
600	1224.00
700	1428.00
800	1632.00
900	1836.00
1000	2040.00

FPS to GPM Conversion Chart

Pipe Diameter (inches)	Flow Velocity (FPS)	Calculated GPM
1	1	7.48
1	2	29.92
1	3	67.25
1	4	120.70
1	5	193.25
2	1	29.92
2	2	119.68
2	3	268.31
2	4	477.46
2	5	740.98
3	1	67.25
3	2	268.31
3	3	602.44
3	4	1077.93
3	5	1680.83
4	1	120.70
4	2	477.46
4	3	1077.93
4	4	1925.52
4	5	3038.06
6	1	272.34
6	2	1089.36
6	3	2440.67
6	4	4320.00
6	5	6480.00

FPS to GPM Conversion Formula

The formula for converting FPS to GPM is:

GPM = FPS × (Pipe Area in sq. ft) × (448.83 gal/min/cfs)

Where:

• FPS = Flow velocity in feet per second
• Pipe Area = π × (pipe diameter in feet)² ÷ 4
• 448.83 = Conversion factor from cubic feet per second to gallons per minute

For a 6-inch (0.5 ft) diameter pipe with 3 FPS flow:

Pipe Area = π × (0.5 ft)² ÷ 4 = 0.196 sq. ft
GPM = 3 × 0.196 × 448.83 = 264.37 GPM

How to Convert FPS to GPM?

Converting FPS to GPM involves these step-by-step calculations:

• Determine pipe diameter in feet: 8-inch (0.667 ft)
• Calculate pipe cross-sectional area:
• Multiply by flow velocity in FPS
• Apply the conversion factor

Converting 4 FPS in an 8-inch (0.667 ft) diameter pipe:

• Area = π × (0.667)² ÷ 4 = 0.349 sq. ft
• Flow = 4 FPS × 0.349 × 448.83 = 626.97 GPM

How do you convert flow rate to GPM?

Converting various flow rates to GPM requires different conversion factors:

• From cubic feet per second (CFS): Multiply by 448.83
• From liters per minute (LPM): Multiply by 0.264172
• From cubic meters per hour (m³/h): Multiply by 4.402868

Example:

Converting 0.5 CFS to GPM:

GPM = 0.5 × 448.83 = 224.415 GPM

What is FPS in water?

FPS in water refers to the linear velocity of water flow measured in feet per second.

In a residential water supply system, typical flow velocities range from 4-8 FPS:

Recommended velocity = 6 FPS
Maximum velocity = 8 FPS (to prevent erosion)
Minimum velocity = 2 FPS (to prevent sediment)

Sources:

• U.S. Geological Survey Water Resources https://www.usgs.gov/mission-areas/water-resources

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