Method of predicting a lifetime of a gas filling of an electrical switchgear, comprising the steps of a) measuring a first pressure value p 1 in a system of the electrical switchgear containing the gas filling at a predefined temperature T p at a first point in time t 1 and measuring a second pressure value p 2 in the system of the electrical switchgear containing the gas filling at the same predefined temperature T p at a second point in time t 2 or b) measuring a first pressure value p 1 in a system of the electrical switchgear containing the gas filling at a first temperature T 1 within a predefined temperature range at a first point in time t 1 and measuring a second pressure value p 2 in the system of the electrical switchgear containing the gas filling at a second temperature T 2 within the same predefined temperature range at a second point in time t 2, - calculating a pressure difference Δp between the first pressure value p 1 and the second pressure value p 2 and characterized in that the method further comprises the steps of: - calculating a total lifetime of the gas filling based on said pressure difference Δp, wherein the first pressure value p 1 and/or the second pressure value p 2 is calculated based on a volume change of a capacitor having an elastomer as a dielectric material between two electrodes (6, 7) of the capacitor, and - wherein the total lifetime LT total of the gas filling is calculated using the formula: LT total = Δ t ⋅ p high − p low Δ p = t 2 − t 1 ⋅ p high − p low p 2 − p 1 wherein p low is a predefined minimum pressure value of the gas filling, p high is the initial pressure value of the gas filling, and Δt is the time difference between the second point in time t 2 and the first point in time t 1. a) measuring a first pressure value p 1 in a system of the electrical switchgear containing the gas filling at a predefined temperature T p at a first point in time t 1 and measuring a second pressure value p 2 in the system of the electrical switchgear containing the gas filling at the same predefined temperature T p at a second point in time t 2 or b) measuring a first pressure value p 1 in a system of the electrical switchgear containing the gas filling at a first temperature T 1 within a predefined temperature range at a first point in time t 1 and measuring a second pressure value p 2 in the system of the electrical switchgear containing the gas filling at a second temperature T 2 within the same predefined temperature range at a second point in time t 2, - calculating a pressure difference Δp between the first pressure value p 1 and the second pressure value p 2 and characterized in that the method further comprises the steps of: - calculating a total lifetime of the gas filling based on said pressure difference Δp, wherein the first pressure value p 1 and/or the second pressure value p 2 is calculated based on a volume change of a capacitor having an elastomer as a dielectric material between two electrodes (6, 7) of the capacitor, and - wherein the total lifetime LT total of the gas filling is calculated using the formula: LT total = Δ t ⋅ p high − p low Δ p = t 2 − t 1 ⋅ p high − p low p 2 − p 1 - calculating a pressure difference Δp between the first pressure value p 1 and the second pressure value p 2 and - calculating a total lifetime of the gas filling based on said pressure difference Δp, wherein the first pressure value p 1 and/or the second pressure value p 2 is calculated based on a volume change of a capacitor having an elastomer as a dielectric material between two electrodes (6, 7) of the capacitor, and - wherein the total lifetime LT total of the gas filling is calculated using the formula: LT total = Δ t ⋅ p high − p low Δ p = t 2 − t 1 ⋅ p high − p low p 2 − p 1