Jacques Charles studied the relationship between volume (V) and temperature (T) of a confined gas at constant pressure and saw how gas tend to increase in volume when heated. He observed that the ratio of volume and temperature remains nearly constant which can be given as:
V / T = constant = k (say)
V1 / T1 = V2 / T2
V1 . = V2 *T1
Charles Law  

where,
V_{i} = Initial Volume,
T_{i} = Initial Temperature,
V_{f} = Final Volume.
T_{f} = Final Temperature,
Example:
Calculate the Final Temperature (T_{f}) by using the Charlesâ€™ Law Calculator.
Initial Volume (V_{i}) = 25 L
Initial Temperature (T_{i}) = 5 K
Final Volume (V_{f}) = 15 L
Solution:
Apply Formula:
Gas Equation: V_{i}/T_{i} = V_{f}/T_{f} or V_{f}/V_{i} = T_{f}/T_{i} or V_{i}T_{f} = V_{f}T_{i
}Final Temperature (T_{f}) = 3 K