Two questions are likely to be asked about this report. First, are these calculated differences really relevant? And second, might the authors’ findings serve to explain why one clinical trial of lower tidal volume in ARDS might be successful and another not? The latter question cannot be answered with certainty, but use of an overall lower tidal volume is one plausible explanation for the lower mortality and shorter time on ventilation seen in the ARDS Network trial but not in all studies of lung protective ventilation. One skeptical of this possibility could argue that if the tidal volume derived from a given equation were too large it would be reduced when the resulting plateau pressure exceeded the recommended target. Unfortunately, in practice, plateau pressures are not always measured or acted upon, and lower tidal volumes might offer benefits even if the plateau pressure did not exceed a recommended threshold. The answer to the first question, however, is almost certainly yes; tidal volume differences of 30% could amount to > 100 mL of inflation for some patients and almost certainly could contribute to volutrauma in vulnerable individuals. Fortunately, lower, or perhaps more accurately described as normal, tidal volumes determined using predicted body weight have now become widely accepted for care of many patients who are ventilated with and without ARDS.7,8 But the question remains: Which equation should be used? Undoubtedly, the authors’ recommendation that the predicted body weight equations used by the ARDS Network become the “industry standard” will generate controversy among some readers who will claim that we do not know those equations are the “best.” While it is clear that we do not know if the equations used by the ARDS Network will be the best choice forever, it is clear that for now, they are the best we know.