This paper reinvestigates the compliance equation used in ASTM E1820, Standard Test Method for Measurement of Fracture Toughness, for compact tension (C(T)) specimens. It is found that the elastic compliance equation is inconsistent with that determined from the stress intensity factor (K) solution that is also used in ASTM E1820 for the same compact specimens. Because the K solution in ASTM E1820 is very accurate, as verified by different finite element analysis (FEA) results, the compliance equation in ASTM E1820 can be less accurate, making it necessary to develop a more accurate solution. Using the shooting method and an accurate FEA result of elastic compliance at a/W = 0.5, the more accurate compliance values are obtained for ASTM E1820 C(T) specimens over a wide range of a/W by integration of the accurate K solution. The inverse solution of the new compliance equation is then obtained by curve fitting. The comparison shows that the proposed compliance inverse solution can determine very accurate crack length with negligible errors.