Numbers are thought to be represented in space along a mental left-right oriented number line. Number magnitude has also been associated with the size of grip aperture, which might suggest a connection between number magnitude and intensity. The present experiment aimed to confirm this possibility more directly by using force as a response parameter. Participants judged parity of a single digit by executing a weak or forceful key press. Response selection was faster when small digits required a weak response and large digits required a forceful response than when this mapping was reversed. These findings indicate an effect of number magnitude on the initiation of response intensity. There was no evidence for such an effect on response execution because the actually applied response force was not associated with number magnitude. These findings confirm a previously postulated link between different magnitude domains such as number magnitude and intensity as a basis for action. (Contains 2 figures.)