The ACSM running equation, in plain language
This calculator uses the American College of Sports Medicine running metabolic equation for oxygen cost, then converts oxygen to calories. On the level, running VO2 in mL/kg/min is estimated as 3.5 + 0.2 × speed in meters per minute. When a grade is present, an extra term is added: 0.9 × speed in meters per minute × grade as a fraction. Calories are then VO2 × body mass in kg × time in minutes / 1,000 × 5, using the common planning factor of about 5 kcal per liter of oxygen.
That is a population equation, not a personal lab test. It does not know your running economy, wind, surface, or whether you walked the hills. Two runners at the same pace and body weight can differ by a meaningful number of calories. Treadmill watches and gym consoles use their own models, so a disagreement of 10–20% is not unusual and is not automatically a bug.
The equation is intended for running, not walking. For a walk, use the walking calorie calculator, which is built on Compendium MET values, or the ACSM walking equation described on that page’s sister tools. If you have a step count rather than a pace, try the steps to calories calculator.
Grade matters more than many people expect. A modest incline raises oxygen cost quickly because of the 0.9 × speed × grade term. A downhill is not handled here — the ACSM running equation as implemented is for level or uphill work. Outdoor routes also add air resistance that a still treadmill does not; some coaches set a 1% treadmill grade as a rough outdoor stand-in. That 1% trick is a convention, not a term hidden inside the official equation, so this page only applies the grade you type.
These calories are an energy-cost estimate for the session, not a promise of fat loss. Daily intake, the TDEE calculator, and a conservative calorie deficit plan sit in a different layer than a single run. This is not medical advice, and hard running in heat or with symptoms is a reason to stop, not to chase a calorie target.
Frequently asked questions
Does a faster pace always burn more calories?
At a fixed duration, yes — the ACSM speed term rises with pace, so a faster 30 minutes costs more than a slower 30 minutes for the same body weight. At a fixed distance, the picture is milder: you finish sooner, and economy and rest afterward still matter. The calculator shows both the session total and a per-hour rate so you can see the difference.
Can I use this for a treadmill class or hiking?
Use it for running or jogging on a treadmill or road, with the grade you actually used. Hiking or a walk-run with a lot of walking is closer to a walking or mixed-MET estimate. Steep hiking with a pack is outside this equation.
Why is my watch different?
Watches may mix heart rate, personal history, and a different oxygen-to-calorie factor. This page shows the ACSM running equation with a 5 kcal/L conversion and the inputs you entered. Neither number is a chamber measurement.
Should I eat back these calories?
That is a planning choice, not a formula. Many people who are cutting weight do not eat the entire estimate back, because estimates run high for some runners and because appetite and daily movement also move. Use a weekly average from the TDEE and deficit tools rather than one run.
Is the 5 kcal per liter factor exact?
No. The energy equivalent of oxygen varies a little with fuel mix (more carbohydrate versus more fat). Five kilocalories per liter is a widely used planning constant. Changing it would move every result by the same percentage and would not make the estimate “lab accurate.”