While many studies have investigated duration discrimination in human adults and in nonhuman animals, few have investigated this ability in infants. Here, we report findings that 6-month-old infants are able to discriminate brief durations, and, as with other animal species, their discrimination function is characterized by Weber's Law: proportionate difference rather than absolute difference between stimuli determined successful discrimination. Importantly, paralleling results found with nonhuman animals, the Weber function that we found for infants' discrimination of time is the same as that found for their discrimination of number. Infants discriminated durations of an audiovisual event differing by a 1:2 ratio, but not those differing by a 2:3 ratio, over a range of durations. This suggests that (a) in human as in nonhuman animals, the same mental mechanism may underlie the ability to measure duration as to represent number, and (b) we may share this mental mechanism with other animal species.