To quantify how many patient scheduled hours would result in a 40-h work week (PSH40) for ambulatory physicians and to determine how PSH40 varies by specialty and practice type. We calculated PSH40 for 186188 ambulatory physicians across 395 organizations from November 2021 through April 2022 stratified by specialty. Median PSH40 for the sample was 33.2 h (IQR: 28.7-36.5). PSH40 was lowest in infectious disease (26.2, IQR: 21.6-31.1), geriatrics (27.2, IQR: 21.5-32.0) and hematology (28.6, IQR: 23.6-32.6) and highest in plastic surgery (35.7, IQR: 32.8-37.7), pain medicine (35.8, IQR: 32.6-37.9) and sports medicine (36.0, IQR: 33.3-38.1). Health system leaders and physicians will benefit from data driven and transparent discussions about work hour expectations. The PSH40 measure can also be used to quantify the impact of variations in the clinical care environment on the in-person ambulatory patient care time available to physicians. PSH40 is a novel measure that can be generated from vendor-derived metrics and used by operational leaders to inform work expectations. It can also support research into the impact of changes in the care environment on physicians' workload and capacity.