Ball Valve Sizing Chart & Cv Reference | Apex Flow Solutions

Engineers rarely size a ball valve by pipe diameter alone. The number that actually determines whether a valve can pass the required flow at an acceptable pressure drop is the flow coefficient, or Cv. This reference gives Cv values by valve size, explains full-port versus reduced-port behavior, and walks through the Cv calculation so you can verify a valve before you buy it.

Apex Flow Solutions stocks brass, stainless, and PVC ball valves across the full range of port configurations. The data here will help you match valve size and port type to your flow and pressure-drop requirements.

Not sure which port type you need?

Full-port and reduced-port valves of the same nominal size have very different Cv values. If flow capacity is tight, contact our team with your flow rate and allowable pressure drop and we will confirm the right valve.

What Cv Means

The flow coefficient (Cv) is defined as the number of US gallons per minute (GPM) of 60°F water that will flow through a valve with a pressure drop of 1 PSI across it. A valve with a Cv of 25 passes 25 GPM of water at a 1 PSI differential. The higher the Cv, the more flow a valve can pass for a given pressure drop. Cv is the single most useful number for comparing valves of different sizes, port types, and designs, because it captures the real flow restriction rather than just the nominal connection size.

Cv is a dimensionless coefficient in US units. The metric equivalent is Kv (cubic meters per hour at 1 bar drop); the conversion is Cv = 1.156 × Kv, or Kv = 0.865 × Cv.

Cross-section of a full-port and reduced-port ball valve compared side by side

Full-port (left) versus reduced-port (right) ball valves at the same nominal size. The reduced-port bore is one pipe size smaller, lowering Cv and raising pressure drop.

Full Port vs Reduced Port

A full-port (full-bore) ball valve has a ball bore equal to the inside diameter of the matching pipe, so flow passes through with almost no restriction. A reduced-port (standard-port) valve has a bore roughly one pipe size smaller — a 1" reduced-port valve may have the bore of a 3/4" valve. Reduced-port valves cost less and are perfectly adequate for on/off isolation where a modest pressure drop is acceptable, but their Cv is substantially lower. When flow capacity or pressure drop is critical, specify full port.

Ball Valve Cv & Port Size Chart

Representative Cv values for two-piece brass and stainless ball valves. Values are typical; always confirm against the specific manufacturer's data sheet, as Cv varies by body design.

Valve Size (NPT)	Full-Port Bore	Full-Port Cv	Reduced-Port Bore	Reduced-Port Cv
1/4"	1/4"	8	3/16"	5
3/8"	3/8"	14	1/4"	8
1/2"	1/2"	22	3/8"	14
3/4"	3/4"	42	1/2"	22
1"	1"	75	3/4"	42
1-1/4"	1-1/4"	120	1"	75
1-1/2"	1-1/2"	180	1-1/4"	120
2"	2"	360	1-1/2"	180
3"	3"	800	2-1/2"	560
4"	4"	1500	3"	800

The Cv Sizing Formula

To size a valve, calculate the Cv your application requires, then select a valve whose published Cv exceeds it with margin. For liquids (turbulent, non-flashing flow), the formula is:

Cv = Q × √(SG / ΔP)

Where Q = flow rate in GPM, SG = specific gravity of the fluid (water = 1.0), and ΔP = pressure drop across the valve in PSI. Example: to pass 60 GPM of water (SG = 1.0) with a target pressure drop of 2 PSI, required Cv = 60 × √(1.0 / 2) = 60 × 0.707 = 42.4. A 3/4" full-port valve (Cv 42) is right at the edge; a 1" full-port valve (Cv 75) gives comfortable margin. Always size for some headroom — selecting a valve at exactly the calculated Cv leaves no allowance for fouling or future flow increases.

Approximate Flow Capacity by Size

The table below estimates water flow through a fully open full-port ball valve at two common pressure drops, derived from the Cv values above (Q = Cv × √(ΔP) for water).

Valve Size	Full-Port Cv	Flow @ 1 PSI (GPM)	Flow @ 5 PSI (GPM)
1/2"	22	22	49
3/4"	42	42	94
1"	75	75	168
1-1/2"	180	180	402
2"	360	360	805

Note that ball valves are on/off devices. These flow figures apply at the fully open position. Ball valves should not be used for throttling — a partially open ball erodes the seats and the relationship between handle angle and flow is highly nonlinear. For modulating flow control, use a globe or needle valve.

Bar chart of ball valve Cv values increasing with valve size

Cv climbs steeply with size. Doubling the nominal size of a full-port ball valve roughly quadruples its flow capacity.

Standards & References

Ball valve pressure-temperature ratings and dimensions are governed by ASME B16.34 (valves — flanged, threaded, and welding end) and MSS SP-110 (ball valves, threaded and welding end). The flow-coefficient test method is defined in ISA-75.02 / IEC 60534-2-3. Threaded end connections follow ASME B1.20.1 (NPT). For potable water service, confirm the valve carries NSF/ANSI 61 and NSF/ANSI 372 (lead-free) certification.

Frequently Asked Questions

What is the Cv of a 1 inch ball valve?

A 1" full-port ball valve typically has a Cv of around 75, while a 1" reduced-port valve is closer to 42 (the equivalent of a 3/4" bore). Always confirm against the manufacturer's data sheet.

How do I calculate the right ball valve size?

Calculate required Cv with Cv = Q × √(SG / ΔP), then choose a valve whose published Cv exceeds your result with margin. Size by Cv, not by pipe diameter alone, when flow or pressure drop matters.

What is the difference between full port and reduced port?

A full-port valve's bore matches the pipe ID for minimal restriction. A reduced-port valve's bore is about one size smaller, lowering Cv and raising pressure drop. Use full port when flow capacity is critical, reduced port for economical on/off isolation.