A method and apparatus that utilizes a force-time integral for real time estimation of lesion (46) size in catheter-based (32) ablation systems (30). The apparatus measures the force exerted by a contact ablation probe (36, 38) on a target tissue (40) and integrates the force over an energization time of the ablation probe. The force-time integral can be calculated and utilized to provide an estimated lesion (46) size (depth, volume and/or area) in real time. The force-time integral may also account for variations in the power (42) delivered to the target tissue (40) in real time to provide an improved estimation of the lesion (46) size. In one embodiment, the force metric can be used as feedback to establish a desired power level delivered to the probe ( 36, 38) to prevent steam popping.
