How to use the treadmill vs outdoor run intensity calculator
Enter a speed and grade for the treadmill and for the outdoor run and the tool prints oxygen uptake and METs for both side by side, then states the gap as a value and as a percentage. The solved figure underneath answers a different question: holding the treadmill speed where it is, what grade would match the outdoor oxygen uptake. Enter identical conditions and the difference reads 0.0 while the solved grade comes back equal to the outdoor grade.
The maths uses the ACSM metabolic equations. Walking is VO2 = 0.1xS + 1.8xSxG + 3.5 and running is VO2 = 0.2xS + 0.9xSxG + 3.5, where S is metres per minute and G is the grade as a decimal. Entered miles per hour are converted to metres per minute internally and a 2 percent grade becomes 0.02. METs divide oxygen uptake by 3.5, and the difference and the solved grade are computed from the one-decimal values shown on screen so the numbers and the verdict always point the same way (checked October 2026).
The limits matter. Air resistance, the main reason a treadmill feels easier, has no term in the ACSM equations, so matching speed and grade produce matching values. Belt compliance, surface differences and holding the handrails are not modelled either. Temperature, humidity and wind corrections, fluid intake guidance and calorie burn are not outputs of this page, and downhill running sits outside the equations so negative grades are refused.
Frequently asked questions
The same equation is fed the same numbers. The solved treadmill grade also comes back equal to the outdoor grade you typed, which makes it a handy check that the calculation lines up.
Not as a number. The ACSM equations contain no air resistance term, so the cost of pushing through air outdoors is left out and matching speed and grade produce matching values.
No. The ACSM equations cover level and uphill work and do not apply to negative grades. Enter a negative grade and a message appears instead of a result.