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The calculator multiplies the water surface area by a methane factor per trophic stage (kg CH₄ per hectare and year) and converts it into CO₂ equivalents using the global warming potential. The stages follow the 1998 LAWA trophic classification by seasonal mean chlorophyll-a: oligotrophic up to 3, mesotrophic up to 9.7, eutrophic up to 31, polytrophic up to 100, hypertrophic above 100 µg/l (eutrophic 1/2 and polytrophic 1/2 are each combined). The methane factors are calculated from the regression in DelSontro et al. 2018 at these class boundaries: log₁₀ CH₄ = 0.778 · log₁₀ Chl-a + 0.940 (mg CH₄-C per m² and day), converted from carbon to methane (× 16/12) and to hectares and years; this gives 42 to 2,619 kg of methane per hectare and year from oligotrophic to hypertrophic. For the open-ended outer classes, 1 and 200 µg/l are set as calculation limits; above 100 µg/l this is an extrapolation. The global warming potential is that of biogenic methane in IPCC AR6: 27 over 100 years, 79.7 over 20 years. Only methane is counted – CO₂ and nitrous oxide are not included; according to DelSontro et al., methane accounts for roughly three quarters of the climate impact of lakes. The car equivalent uses a reference value of around 2 t CO₂ per car and year. All figures are orders of magnitude for context – not a substitute for a water-body-specific emissions balance.