Use the highest
temperature that the beer saw towards the end of (or after) fermentation.
A couple scenarios:
1) Pitch at 65, free rise to 72 during ferment, cold crash at 34 Use 72 degrees
2) Pitch and ferment at 68, store the carboy in your 60 degree basement for a month of bulk aging Use 68 degrees
3) Pitch at 50, ferment at 55, D-rest at 68, lager at 33 Use 68 degrees
4) Pitch at 50, ferment at 55, no D-rest, lager at 33 Use 55 degrees
5) Pitch and ferment at 62 in a fermentation chamber, after fermentation is over toss the carboy in a 70 degree closet for 2 weeks Use 70 degrees
The calculators can make a good approximation of how much residual CO2 is in solution. But remember it's all an approximation, so many people (I know Yooper is one
) just add one ounce of corn sugar per gallon of finished beer and call it a day.