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proton mass  Numerical value  1.672 621 923 69 x 10-27 kg  Standard uncertainty  0.000 000 000 51 x 10-27 kg   Relative standard uncertainty  3.1 x 10-10  Concise form  1.672 621 923 69(51) x 10-27 kg       Click here for correlation coefficient of this constant with other constants Source: 2018 CODATA      recommended values  Definition of uncertainty       Correlation coefficient with any other constant