Ohio Revised Code Title XXIX. Crimes Procedure § 2947.151

(A) On sentences of ninety days or less, up to three days for each thirty days of sentence;

(B) On sentences longer than ninety days but not longer than six months, up to four days for each thirty days of sentence;

(C) On sentences longer than six months, up to five days for each thirty days of sentence.

The reduction of the inmate's sentence, shall become effective only upon the written concurrence of the presiding or sentencing judge or magistrate of the court where the sentence was imposed.

This section shall in no way restrict any other powers vested in the presiding or sentencing judge or magistrate of the court where the sentence was imposed.