This letter is intended to help users select an appropriate calculator for a landscape-scale greenhouse gas (GHG) assessment of activities for agriculture and forestry. Eighteen calculators, which were designed for different aims, were assessed. They are intended to be used in different geographical areas and which use different accounting methodologies. The classification proposed is based on the main aims of the assessment: raising awareness, reporting, project evaluation and product assessment. After establishing the aims, the most suitable calculator can be selected from the comparison tables, accounting for the geographical area, scope of the calculation and the time and skills required for the calculation.