We find a strong correlation between the optical outburst amplitude and orbital period for the soft X-ray transient sources with orbital periods less than 1 d. By fitting the observed values for eight X-ray transients, we determine an empirical relation that can be used to predict the orbital period of an X-ray transient given only its outburst amplitude. For periods less than 12 h we determine a relation for the absolute magnitude of the accretion disk during outburst, which then allows us to estimate the distances to the sources.