Cobalt‐60 dose determination can be accomplished by a variety of methods. This study investigates dose determination by actual “at‐depth” measurement for the depths and field sizes desired as well as by “in‐air” or “in‐water” calibration measurements for both constant SSD and isocentric techniques. Comparison of the above dose determination methods reveals the existence of both depth‐dependent and field size‐dependent dose discrepancies between the individual methods studied. For many teletherapy units, the source of these discrepancies lies in the inapplicability of the tabulated percent depth dose and tissue‐air ratio values employed. Appropriate percent depth dose and tissue‐air ratios can be obtained by performing a series of at‐depth dose determinations for a variety of depths and field sizes. When the appropriate values are employed, excellent agreement is found between all of the dose determination methods investigated.