Despite the superficial penetration of the light, the continuous wave (cw) CO2 laser may induce a relatively large area of thermal damage in tissue next to the ablation crater. Ultra-pulsed laser systems, however, deliver pulse energies above the ablation threshold for tissue within a few hundred microsecond(s) , which instantly vaporize tissue. Since cw ablation models cannot be applied on pulsed ablation, a new model is introduced which is validated experimentally on phantom tissue. It discriminates between the cross section of the laser beam above the ablation threshold and the flanks of beam below threshold inducing thermal effects. Depending on pulse energy and beam diameter, the shape of the ablation crater in the tissue was calculated and validated experimentally in phantom tissue using a pulsed CO2 laser and an Erbium laser. The diameter of the spot varied from 0.1 to 2.5 mm and the pulse energy from 25 to 250 mJ, 10-100 mJ. In the experimental crater depths up to 40 mm could be obtained in one pulse. The theoretical model agreed within 10 to 50 percent with the experimental data for spot sizes form 0.5 to 0.1 mm for the CO2 laser. Although, the thermal effect of these pulses are minimal compared to cw lasers, the sub-threshold part of the laser beam can contribute to undesired thermal damage when repetitive pulses are applied within the thermal relaxation time. The model can serve as a good tool for predicting the depth of ablation for current clinical applications in dermatology, ENT and cardiac-surgery.