When it comes to water flow in pipes, determining the capacity depends on the pipe size and water pressure. Our guide provides handy tables of approximate water flow rates based on pipe size, helping you estimate capacity quickly and easily.

In residential areas, it is required to limit the water flow velocity to a maximum of 8 feet per second (8 ft/s). This is because higher velocities can cause pipe erosion, increase noise, and potentially lead to pressure drops. While specific requirements may vary based on factors such as pipe material, pressure, and fluid properties, it is generally recommended to maintain a flow velocity of no more than 8 ft/s in residential areas.

Attention! Keep in mind, these are only rough calculations. To get more precise estimates, you will need to take additional variables into account, such as temperature and pipe material. With this guide, you’ll have the tools you need to optimize your pipes for maximum efficiency and performance.

Water Velocity in a Pipe – Calculator

Minimum Size for Water Pipe – Calculator

Water Flow Rate in a Pipe – Calculator

Water Flow based on Pipe Size Inside and Outside Diameters

			Assume Gravity to Low Pressure. About 6 f/s flow velocity, also suction side of pump		Assume Average Pressure (20-100PSI). About 12 f/s flow velocity		Assume “High Pressure” PEAK flow. About 18 f/s flow velocity
Pipe Size (Sch. 40)	I.D. (range)	O.D.	GPM (w/ min. PSI loss & noise)	GPH (w/ min. PSI loss & noise)	GPM (w/ min. PSI loss & noise)	GPH (w/ min. PSI loss & noise)	GPM (w/ min. PSI loss & noise)	GPH (w/ min. PSI loss & noise)
1/2″	0.5 – 0.6″	0.85″	7	420	14	840	21	1,260
3/4″	0.75 – 0.85″	1.06″	11	660	23	1,410	36	2,160
1″	1 – 1.03″	1.33″	16	960	37	2,200	58	3,480
1-1/4″	1.25 – 1.36″	1.67″	25	1,500	62	3,750	100	6,000
1-1/2″	1.5 – 1.6″	1.9″	35	2,100	81	4,830	126	7,560
2″	1.95 – 2.05″	2.38″	55	3,300	127	7,650	200	12,000
2-1/2″	2.35 – 2.45″	2.89″	80	4,800	190	11,400	300	18,000
3″	2.9 – 3.05″	3.5″	140	8,400	273	16,350	425	25,500
4″	3.85 – 3.95″	4.5″	240	14,400	480	28,800	700	42,000
5″	4.95″ – 5.05″	5.563″	380	22,800	750	45,000	1,100	66,000
6″	5.85 – 5.95″	6.61″	550	33,000	1100	66,000	1700	102,000
8″	7.96″	8.625″	950	57,000	1900	114,000	2800	168,000

Water Flow Capacity Based on Inside Diameter Size and Pressure

PRESSURE	FLOW IN GPM THROUGH PIPE ID IN INCHES
PSI	1″	1.25″	1.5″	2″	2.5″	3″	4″
20	26	47	76	161	290	468	997
30	32	58	94	200	360	582	1240
40	38	68	110	234	421	680	1449
50	43	77	124	264	475	767	1635
60	47	85	137	291	524	846	1804
75	53	95	153	329	591	955	2035
100	62	112	180	384	690	1115	2377
125	70	126	203	433	779	1258	2681
150	77	139	224	478	859	1388	2958
200	90	162	262	558	1004	1621	3455

Water Flow Capacity in Steel Pipes

Pipe Size	Maximum Flow (gal/min)	Velocity (ft/s)	Head Loss (ft/100 ft)
2″	45	4.3	3.9
2-1/2″	75	5.0	4.1
3″	130	5.6	3.9
4″	260	6.6	4.0
6″	800	8.9	4.0
8″	1,600	10.3	3.8
10″	3,000	12.2	4.0
12″	4,700	13.4	4.0
14″	6,000	14.2	4.0
16″	8,000	14.5	3.5
18″	10,000	14.3	3.0
20″	12,000	13.8	2.4
24″	18,000	14.4	2.1