Ball Valve Sizing Calculator

Knowing how to properly size a ball valve to select the correct one is a crucial first step. Learn how the orifice diameter and pipe connection size help determine the size of a valve. However, you typically need to go a step further than this by calculating the pressure drop of media across the valve and the flow rate for a more accurate valve size. Cv and Kv values are flow coefficients that estimate the media flow rate through a valve. These values help determine the valve size for a given media flow rate. This article discusses the different flow coefficients used for liquids and gasses and also their respective values for various types of ball valves.

Table of contents

• What is flow rate?
• Cv value
• Kv value
• How to measure ball valve size
• Ball valve size chart
• FAQs

What is flow rate?

The flow rate or flow coefficient is the rate at which media flows through a valve and how much the pressure drops from the input to the valve output. The flow rate value can be calculated using the specific formula; a large value means there is a high fluid flow rate through the valve at a given pressure drop.

Depending on the type of measurement system used (imperial or metric), the media flow rate is expressed as Cv or Kv, respectively. The Cv (or Kv) value required is listed in the valve’s product description or specifications label. These values give an idea about the flow rate through a valve in its fully open condition for a given medium and pressure drop. The larger this value, the higher the flow rate through the valve will be at a given pressure drop. Different formulas are used to calculate the Cv (or Kv) values for liquids and gasses, as discussed in the next section. Read our article on flow principles of valves for more information on how to do the measurements for determining flow coefficients.

Cv value

Cv for liquids

The liquid’s inlet and outlet pressures, specific gravity, and flow rate can be used to determine the value of Cv.

• Q: Flow rate in gallons per minute [gpm] at 60^°F
• dp: Pressure differential [psi]
• SG: Specific gravity of the liquid (ratio of the density of the liquid to the density of water)

Hence, the Cv value is defined as the flow rate of water in U.S. gallons per minute (gpm) at a temperature of 60⁰F with a pressure drop of 1 psi across the valve. Cv value is the flow coefficient in the imperial system. Choose a valve with a Cv value equal to or slightly higher than the calculated value.

For example, a valve with a Cv of 15 will pass 15gpm of fluid at 1psi pressure drop across the valve at 60⁰F. The minimum Cv value required for an application can be calculated if the desired flow rate, media characteristics, and pressure drop are known. The larger the opening in a valve, the larger the Cv value. As a valve opens from its fully closed position, its Cv value increases moderately from zero until the valve gets into its fully opened state, where it reaches its highest possible Cv (100% open valve Cv).

Example

To calculate the Cv value of a valve for a water flow of 10 gpm (gallons per minute) with a required differential pressure of 4 psi,

• Q = 10 gpm
• SG = 1
• dp = 4 psi

Hence, the required Cv value is 5. This value can be used to choose an appropriate sizing for the valve which is discussed later in this article.

Cv for gasses

For gasses, the flow coefficient is dependent on the upstream (inlet) and downstream (outlet) pressure and the pressure drop.

If Δp < p1/2:

If Δp > p1/2:

• Cv: Flow coefficient of valve
• G: Specific gravity of gas at flowing conditions
• p1: Upstream (inlet) pressure in psia (psia is absolute pressure)
• p2: Downstream (outlet) pressure in psia
• Δp: Pressure drop (p1-p2) in psi
• Q: Volumetric flow rate, SCFH
• T: Flow temperature in ⁰R (= ⁰F + 460)
• psia = psig +14.7
  • Psig is the pound per square inch gauge. It is a pressure unit relative to the atmospheric pressure.

Kv value

Kv value for liquids

• q: Flow rate[m³/hour]
• Kv: Flow coefficient
• Δp: Pressure differential [bar] at 20⁰C
• G: Specific gravity of the liquid (=1 for water)

The Kv value is defined as the flow rate of water in m³/h with a pressure drop of 1 bar at 20⁰C. Kv value is the flow coefficient in the metric system. Please note that the Kv value is expressed in m³/hour, while the kv value (lowercase) is expressed in l/min. Also, the terms in the equations for Kv and Cv for liquids are similar, except that the parameters are calculated in different measurement systems.

Consider the same example discussed above. To calculate the Kv value of a valve for a water flow of 10 gpm (gallons per minute) with a required differential pressure of 4,

• q = 10 gpm = 10 ✕ 0.0037m³/minute = 10 ✕ 0.0037 ✕ 60 m³/h = 2.22m³/h
• G = 1
• dp = 4 psi = 4 ✕ 0.0689 bar = 0.2756 bar

Therefore, the required Kv value for the given flow rate is 4.22. The Cv or Kv values can be used to determine the valve size required for a particular application. The Cv and Kv values for liquids are related as,

Kv = 0.853 Cv, or,

Cv = 1.16 Kv

Kv value for gasses

Use the following relations to calculate the Kv value of gasses:

• Qn: Normal flow rate [m³/hour]
• T: Inlet gas temperature [K]
• p1: Inlet pressure [bar]
• p2: Outlet pressure [bar]
• Δp: Pressure differential [bar]
• SG: Specific gravity of the gas

Choose a valve with a Kv value equal to or slightly higher than the calculated value. Use the automated Kv calculator on our website to find the Cv values of gasses and liquids.

How to measure ball valve size

Use our Kv calculator to calculate the flow rate required for a given medium and pressure drop. When choosing valves, select a Cv (or Kv) value closest to the calculated result, typically rounding down to the nearest number unless a specified maximum pressure differential of a valve is exceeded. An oversized valve can cause water hammerand premature wear on the valve packaging. Conversely, an undersized valve may not provide enough media flow and exceed available differential pressure between the ports.

Table 1 shows the Cv and Kv values against the various ball valve sizes for three-way reduced port threaded ball valves. If the calculated Cv value is 15, choose a ball valve with ½ inch size as it is closest to the rated Cv value (15.2) for the size. If the calculated Cv value is 110, choose a ball valve size of 2 inches and so on.

Ball valve size chart

The Cv and Kv values of different types of ball valves are given in Tables 1-5.

Full port ball valve Cv chart & Kv chart

Size BSP (in inch)	DN (mm)	Cv when fully open	Kv when fully open
1/4	8	18	15.35
3/8	10	20	17.06
1/2	15	23	19.6
3/4	20	55	46.9
1	25	95	81.03
1 1/4	32	155	132.2
1 1/2	40	260	221.8
2	50	440	375.3
2 1/2	65	710	605.6
3	80	1050	895.6
4	100	2040	1740.1

Table 1: Full port ball valve Cv chart

3-way full bore flanged ball valve Cv & Kv chart

Size (in inch)	Cv	Kv (m3/h)
1/2	15.2	13
3/4	23.3	20
1	45.5	39
1 1/4	58.4	50
1 1/2	112	96
2	224.1	192
2 1/2	308.1	264
3	409.6	351
4	762.1	653

Table 2: 3-way full bore flanged ball valve Cv chart

3-way reduced port threaded ball valve Cv and Kv chart

Size (in inch)	Cv (gallons/min)	Kv (m3/h)
1/4	12.8	11
3/8	12.8	11
1/2	15.2	13
3/4	17.5	15
1	36.2	31
1 1/4	45.5	39
1 1/2	72.4	62
2	120.2	103
2 1/2	239.2	205
3	270.7	232
4	480.8	412

Table 3: 3-way reduced port threaded ball valve Cv and Kv chart

V-port ball valve Cv chart

Valve size (inch)	Ball angle	15%	20%	30%	40%	50%	60%	70%	80%	90%	100%
1/2	300	0.1	0.1	0.2	0.3	0.5	0.8	1.1	1.6	2.2	2.6
	600	0.1	0.1	0.3	0.5	0.9	1.4	2	3.3	4.4	6
3/4	300	0.1	0.2	0.5	0.7	1.1	1.8	2.4	3.3	4.5	5.4
	600	0.1	0.2	0.7	1	1.7	2.8	4	6.5	9	12
1	300	0.1	0.3	0.8	1.3	2.3	3.5	5.1	9.8	8.5	10
	600	0.2	0.4	1.1	1.8	3.4	5.3	7.9	12.3	15.3	21
1 1/4	300	0.2	0.4	1.1	2	3.7	5.5	8	10	13	15
	600	0.2	0.6	1.8	3	5.5	9.5	12.8	19	26	39
1 1/2	300	0.3	0.6	1.6	3	5	7.5	11	14	17	20
	600	0.4	0.8	2.5	4	8	13	19	27	40	52
2	300	0.4	1.2	3.8	6	10	15	23	31	43	60
	600	0.4	1.	4.6	9	16.5	27	39	55	83	110
2 1/2	300	0.4	1	4	8	12	18	28	37	62	75
	600	0.4	1.5	5	10	21	34	53	75	103	150
3	300	0.5	1.2	4	8	14	23	33	46	65	82
	600	0.5	2.5	6	4	25	40	65	91	128	165
4	300	0.6	2	6	15	29	48	71	100	130	159
	600	0.7	3	11	25	40	59	90	141	212	356
6	300	0.9	3.2	14	33	60	103	155	220	280	350
	600	2	5	22	60	110	190	285	416	586	800

Table 4: V-port ball valve Cv dimension chart

V port ball valve Kv chart

(inch)	Ball angle	15%	20%	30%	40%	50%	60%	70%	80%	90%	100%
1/2	300	0.08	0.08	0.17	0.25	0.42	0.68	0.93	1.36	1.87	2.2
	600	0.08	0.08	0.25	0.43	0.77	1.19	1.706	2.8	3.7	5.12
3/4	300	0.08	0.17	0.42	0.6	0.93	1.5	2.04	2.8	3.8	4.6
	600	0.08	0.17	0.59	0.85	1.45	2.4	3.412	5.5	7.7	10.23
1	300	0.08	0.25	0.68	1.1	1.96	2.98	4.3	8.3	7.25	8.53
	600	0.17	0.34	0.93	1.5	2.9	4.5	6.73	10.5	13.05	17.91
1 1/4	300	0.1	0.34	0.94	1.7	3.16	4.7	6.82	8.53	11.1	2.8
	600	0.17	0.51	1.53	2.6	4.7	8.1	10.9	16.2	22.1	33.3
1 1/2	300	0.25	0.51	1.36	2.5	4.2	6.4	9.4	11.9	14.5	17.06
	600	0.34	0.68	2.13	3.4	6.8	11.1	16.2	23.03	34.12	44.3
2	300	0.34	1.02	3.24	5.1	8.5	12.8	19.6	26.4	36.7	51.2
	600	0.3	0.8	3.9	7.7	14.07	23.03	33.2	46.9	70.7	93.8
2 1/2	300	0.3	0.8	3.4	6.8	10.2	15.3	23.9	31.5	52.9	63.9
	600	0.3	1.3	4.3	8.5	17.9	29	45.2	64	87.8	127.9
3	300	0.4	1	3.4	6.8	11.9	19.6	28.1	39.2	55.4	69.9
	600	0.4	2.1	5.1	3.4	21.3	34.1	55.4	77.6	109.2	140.7
4	300	0.5	1.7	5.1	12.8	24.7	40.9	60.5	85.3	110.9	135.6
	600	0.6	2.55	9.4	21.3	34.1	50.3	76.8	120.3	180.8	303.6
6	300	0.7	2.73	11.9	28.1	51.2	87.8	132.2	187.7	238.8	298.5
	600	1.7	4.3	18.7	51.2	93.8	162	243.1	354.8	499.8	682.4

Table 5: V-port ball valve Kv dimension chart

FAQs

What is a Kv value of a valve?

Kv value is a measure of the fluid flow rate through a valve. It is defined as the flow rate of water in m3/h with a pressure drop of 1 bar at 20°C.

What is Cv in valves?

Cv of a valve is the water volume at 60⁰F that flows through the valve when it is fully opened with a pressure differential of 1 psi across the valve.

How do you convert Kv to Cv?

Kv and Cv are related as, Cv = 1.16 Kv.

Is Kv the same as Cv?

Kv (also known as the SI system) is the flow factor in the metric system, whereas Cv is the flow factor in the imperial system.