The Efficiency Calculator determines the efficiency of a system using the formula Efficiency (%)=(Useful Output Energy/Input Energy)×100\text{Efficiency (\%)} = (\text{Useful Output Energy} / \text{Input Energy}) \times 100Efficiency (%)=(Useful Output Energy/Input Energy)×100. By entering any two of the three variables, the calculator computes the unknown. This tool is useful for physics, engineering, and energy studies to evaluate how effectively energy is converted into useful work in machines or processes.