Method: Useful heat required to generate one tonne of steam is: Q_steam = 1000 × (h_steam − h_feedwater) where enthalpy values are in kJ/kg. Feedwater enthalpy is approximated from: h_feedwater ≈ 4.186 × T in kJ/kg for feedwater temperature in °C, referenced approximately to liquid water at 0°C. Fuel energy required is: Q_fuel = Q_steam ÷ η Fuel quantity required is: Fuel Quantity = Q_fuel ÷ Heating Value Fuel cost per tonne of steam is: Fuel Cost = Fuel Quantity × Fuel Price Total steam cost is: Total Cost = Fuel Cost + Additional Direct Cost Fuel heating value and boiler efficiency must be on a consistent basis. For example, an LHV-based boiler efficiency should be used with an LHV fuel heating value, while an HHV-based efficiency should use HHV. Steam specific enthalpy should come from steam tables or suitable process-property data at the actual pressure and temperature. Saturated and superheated steam can have materially different enthalpies. This calculator estimates direct steam-generation cost. It does not automatically include labour, depreciation, electricity for auxiliaries, blowdown heat loss, condensate losses, maintenance, distribution losses or capital cost unless the user incorporates those costs into the additional-cost input.