Simultaneous spacecraft observations of the cusp at large separations are rare, hence estimates of the spatial extent of the cusp are primarily statistical. We attempt to constrain a value for the instantaneous spatial extent by examining data from a joint Cluster-EISCAT campaign on the 7th of April 2013 between approximately 10:00 UT and 13:00 UT during which the separation of the Cluster spacecraft was 1.6Re. We examine the electron differential energy flux, as measured by the PEACE instrument onboard Cluster, to identify periods where multiple spacecraft detect the cusp simultaneously. The spacecraft tetrahedron at one time during this event was found to be entirely contained within the cusp; the spacecraft separation therefore gives a value for the minimum spatial extent the cusp had at that time. Mapping the spacecraft tetrahedron to the ionosphere gives an estimate for the minimum area of the ionosphere that is affected by the cusp which was found to be 1 hour of MLT. EISCAT data is then examined to find that the EISCAT radar observes cusp signatures spanning 3 hours of MLT. During this event EISCAT is located in the post-noon sector but ionospheric flow observations suggest that the reconnection line extends into the pre-noon sector. Reasons for the apparent discrepancy between the in situ and ionospheric determination of the cusp extent is the topic of ongoing work.