The gas dependency ratio is the share of gas imported from Russia over total gas imports, weighted by the share of net imports of gas over total Gross Inland Consumption.
Gross Inland Consumption (GIC) includes consumption by the energy sector, distribution/transformation losses, final energy consumption by end users, and 'statistical differences'. It thus accounts for "gross demand for energy".
Hence, overall dependency is simply net imports of all energy sources over GIC, and gas dependency is net gas imports over GIC.
We use Eurostat 2019 data for net imports of energy and GIC, and Bruegel 2021 data for the share of gas imported from Russia, due to a lack of data on Russian imports for some key countries in Eurostat (among which Ukraine).