The influence of inoculum size on the growth of keratinocyte cells was investigated in a monolayer culture with serum-free medium. A growth model of cell placement was applied to the expression of the cell adhesion phase after the inoculation, lag phase, exponential growth phase, and stationary phase because of contact inhibition at high cell densities. Based on the model, the lag time until the onset of cell division was shortened in proportion to the logarithm of the inoculum cell size, resulting in the enhancement of overall cell propagation. It was verified that the proposed model is valid for the determination of the optimal inoculum size to realize the efficient growth of keratinocytes, indicating that the model is a useful tool to predict an optimal culture scheme for the production of skin grafts.