How does the calculator work out the pressure?

It uses a regression of CO2 solubility in beer that takes temperature in degrees Fahrenheit and the target volumes of dissolved CO2, returning the gauge pressure needed to hold that level at equilibrium. Colder beer holds more CO2, so it needs less pressure for the same carbonation.

What are volumes of CO2?

One volume of CO2 means one volume of dissolved carbon dioxide gas per volume of beer at standard conditions. It is the standard brewing unit for carbonation. One volume is roughly 1.96 grams of CO2 per litre of beer.

How long does force carbonation take at this pressure?

Set-and-forget at the calculated pressure typically takes 5-10 days to reach equilibrium. You can speed it up by shaking the keg or raising the pressure temporarily, but the set-and-forget method gives the most consistent, repeatable result.

Why is my beer foaming even at the right pressure?

Foaming at the correct carbonation pressure is almost always a serving-line problem, not a carbonation one. The line must add enough resistance to balance the keg pressure. Use longer or narrower beer line so the pour pressure drops to near zero at the tap.

Does the temperature mean the freezer or the beer?

Always the beer temperature. Carbonation reaches equilibrium with the liquid, so use the temperature of the beer itself after it has settled. The freezer or fridge setpoint is only an approximation of the final beer temperature.

Keg Carbonation (CO2) Calculator

The Keg Carbonation Calculator tells you exactly what pressure to set your CO2 regulator to so a keg reaches and holds a target level of carbonation at a given serving temperature. It replaces the dog-eared carbonation chart taped to the side of every kegerator with a precise, instant number.

How it works

CO2 dissolves into beer until it reaches equilibrium with the headspace pressure. The amount that stays in solution depends on two things: the temperature of the beer and the gauge pressure applied. Colder beer holds more gas, so it needs less pressure for the same carbonation level.

The calculator uses the standard brewing regression that maps temperature (in degrees Fahrenheit) and target volumes of CO2 to the required gauge pressure:

PSI = -16.6999
      - 0.0101059 * T
      + 0.00116512 * T^2
      + 0.173354 * T * V
      + 4.24267 * V
      - 0.0684226 * V^2

where T is the beer temperature in degrees Fahrenheit and V is the target volumes of dissolved CO2. The result is the gauge pressure (PSI) to dial into your regulator. The tool also converts that to bar and kilopascals, and shows the dissolved CO2 in grams per litre (one volume is about 1.96 g/L).

Worked example

A standard American pale ale served at 38 °F with a target of 2.5 volumes:

Plug T = 38 and V = 2.5 into the formula.
The regression returns about 11 PSI.
Set the regulator to 11 PSI, leave the keg connected for a week, and it will hold 2.5 volumes indefinitely.

The same beer at a warmer 45 °F needs roughly 13 PSI for the same carbonation, because warmer beer holds less gas at a given pressure.

Tips and serving-line notes

Getting the carbonation right is only half the battle. If the beer pours all foam, the problem is usually line balance, not carbonation. Your serving line must add enough resistance to drop the keg pressure to near zero at the tap. As a rough rule, 3/16 inch inner-diameter vinyl line adds about 2-3 PSI of resistance per foot. A keg at 11 PSI typically wants 5-6 feet of 3/16 inch line for a clean, balanced pour. Too short and the pour foams; too long and it trickles. Always let the keg reach equilibrium before judging the pour, and keep the beer temperature stable, since carbonation tracks temperature directly.