A sub-4:00 marathon needs an average pace of about 5:41 per km, or 9:09 per mile, held for the full 42.195 km (26.2 miles).
A 3:30:00 marathon needs about 8:01 per mile, or 4:59 per km. Small buffer aside, that pace held evenly gets you to the finish just under 3 hours 30 minutes.
It's a common and widely respected benchmark: finishing under 4 hours means averaging roughly 9:09 per mile, faster than a large share of marathon finishers at most big-city races. Whether it's realistic for you depends on training volume and a recent shorter race result, which the race time predictor can help estimate.
A sub-3:00 marathon needs about 4:16 per km, or 6:52 per mile, for the full distance. That pace matches the Boston Qualifying standard for men 35-39 (3:00:00), though it falls just short of the fastest standard on the board, men 18-34 at 2:55:00.
Splits assume perfectly even pacing: every 5 km (or every mile, depending on your unit) multiplied by the required pace, with a final row at the full marathon distance. Real races rarely run dead even, so treat these as a pacing reference rather than a race-day prediction.
It depends on your age and sex. This tool notes how your goal time compares to the published Boston Qualifying standards. For a full check across all eight Abbott World Marathon Majors, use the Qualification Checker with your goal time.