In this paper, we propose TSProbe, a new capacity estimation technique for time-slotted wireless systems. Although inspired by Adhoc Probe, the design of TSProbe is tailored to time-slotted connections. Unlike legacy approaches that rely on probes of identical size, TSProbe takes advantage of the intrinsic relationships between various link layer properties, and deploys an adaptive and iterative probing scheme that is both efficient and accurate. We analyze the theoretical basis of TSProbe, and evaluate its performance in a variety of simulation scenarios. The results show that the technique is consistently accurate and effective in all cases.