Touch-sensitive surfaces are already a standard form of interaction. These surfaces come in many different sizes like tablets or touch walls. However, there is little research to characterize the impact of surface size on touch performance. We conducted a Fitts’ Law study of three display sizes (13.5" tablet, 28" monitor, 69.5" large monitor), comparing various performance measures. We found that the smallest size (13.5" is problematic both objectively (high error rate) and subjectively (imprecise, difficult-to-use). In contrast, both the medium (28") and the large display (69.5") perform equally well. However, small displays allow for greater interaction speed compared to very large screens. Our results can help interaction designers and automatic algorithms to optimize current and future touch devices.