Induction motors fail due to many reasons, and many are rewound two or more times during their lifetimes. It is generally assumed that a rewound motor is not as efficient as the original motor. Precise estimation of efficiency of a refurbished motor or any existing motor is crucial in industries for energy savings, auditing, and management. Full-load and partial-load efficiency can be measured by using the dynamometer. This paper presents a novel technique for estimating refurbished induction motors' full-load and partial-load efficiencies from only no-load tests. The technique can be applied in any electric motor workshop and eliminates the need for the dynamometer procedure. It also eliminates the need for the locked-rotor test. Experimental and field results of testing eight induction motors are presented, and the degree of accuracy is shown by comparing the estimated efficiencies against the measured values. To provide the necessary credits to the proposed technique, an error analysis is conducted to investigate the level of uncertainty through testing three induction motors, and the results of uncertainty of the direct measurements and no-load measurements using the proposed technique are presented.