To streamline the weighing while relatively improving a precision.

A weight estimating method for a tire component member is a method of numerically calculating the weight of at least one component member of a 1st tire as follows: a step in which an area S1 of at least one component member of the 1st tire is calculated from a meridian section of the tire; a step of calculating an area S2 of the component member from the meridian section of a 2nd tire, the weight of the component member of which is previously known and having same size as the 1st tire; and a step of calculating the weight W1 of the component member of the 1st tire by multiplying the weight W2 of the component member of the 2nd tire by an area ratio (S1/S2).