The calorie (otherwise known as food calorie, dietary calorie, or kilogram calorie) is defined as the amount of heat needed to raise the temperature of one kilogram of water by one degree Celsius. This unit measure of energy is a hot topic when it comes to fitness and weight loss. After all, measuring calories can be a useful way to manage energy balance and weight.
So, how many calories should you actually burn during a workout? Read on to learn how to most accurately determine your calorie expenditure and what activities may be best for you.
Well, How Many Calories Should You Burn During a Workout?
The number of calories you should burn during a workout completely depends on your overall fitness goals. When trying to improve strength, speed, power, muscle mass, flexibility, agility, etc. the caloric expenditure will be a by-product of the workout, but not the ultimate focus.
If weight loss or weight gain is your primary goal, specific caloric measurements (of intake and expenditure) are more important to measure. A caloric deficit of 3,500 calories will lead to 1lb of weight loss. Conversely, an excess 3,500 calories will lead to 1lb weight gain. If you are aiming for losing a pound per week, a deficit of 500 calories daily is ideal. This can be done by reducing caloric intake by 250 calories daily and doing a workout that burns a minimum of 250 calories. This equation can be manipulated by how many calories you burn during your workouts and what your caloric deficit is every day.
What Influences How Many Calories You Burn?
Generally, the following factors influence how many calories you burn:
- Body size and composition
- Intensity of exercise
- Type of exercise
- Duration of exercise
- Age and gender
- Fitness level
Calculating the actual number of calories burned during a workout is quite complicated because there are so many factors that influence this number. The main ones are:
- Body size and composition: The more you weigh, the more calories you'll burn during exercise, because your body has to work harder to move your mass. Also, because muscle is a more metabolically active tissue than fat, greater amounts of muscle mass will also lead to a higher calorie burn.
- Intensity of exercise: Higher intensity exercise requires more energy and burns more calories. Exercises that get your heart rate up and make you sweat, such as high-intensity interval training (HIIT), can burn more calories than lower-intensity workouts.
- Type of exercise: Different types of exercises burn different amounts of calories. In general the more muscles you engage, the more calories you burn.
- Duration of exercise: The longer you exercise, the more calories you'll burn. However, shorter, high-intensity workouts can also be effective for burning calories.
- Age and gender: Men and women burn calories at different rates, and metabolism tends to slow down with age, meaning older adults burn fewer calories during exercise than younger adults.
- Fitness level: The fitter you are, the more efficiently your body burns calories, meaning you may burn fewer calories during the same workout as someone who is less fit.
- Genetics: Some people are simply born with a faster metabolism, meaning they naturally burn more calories than others during exercise.
How to Measure Calories Burned
There are several ways you can measure how many calories you burn during a workout. Here are the three most effective methods:
Fitness Trackers and Fitness Apps
Fitness trackers such as your Apple, Garmin, or FitBit smartwatch typically work by using sensors to track your movement, heart rate, and other physical activity. Fitness trackers work with motion sensors, GPS, heart rate sensors and manual input.
Once the app collects data about your physical activity, it typically displays this information in a user-friendly format, such as graphs or charts. Some apps may also provide insights and recommendations based on your activity level and goals. Other fitness apps, such as MyFitnessPal, can connect to these wearables or rely on manual input to help calculate daily caloric expenditure.
MET Value Charts
A more specific and detailed form of measurement, MET (metabolic equivalent of task) value charts can be helpful in estimating the number of calories burned during physical activity. MET is a unit of measurement that indicates the amount of energy expended during an activity compared to resting metabolic rate.
The MET value for an activity is determined by measuring the oxygen consumption during the activity and comparing it to the oxygen consumption at rest. A higher MET value indicates a higher level of energy expenditure.
MET value charts provide a reference for the estimated energy expenditure of various activities. The chart typically lists activities in order of their MET values, with higher values indicating more strenuous activities. The “Compendium of Physical Activities”, detailing MET values for 821 physical activities, was updated in 2011. 
To use a MET value chart to estimate calorie burn, you would need to know your own weight and the duration of the activity. You can then calculate the number of calories burned by multiplying your weight in kilograms by the MET value for the activity and the duration of the activity in hours.
For example, if you weigh 70 kg and you engage in a 30-minute activity with a MET value of 6 (such as bicycling at a moderate pace), you would burn approximately 245 calories. This is calculated as follows:
Calories burned = (70 kg) x (6 METs) x (0.5 hours) = 245 calories
It's important to note that MET values are estimates and may not be completely accurate for every individual. However, they can be a helpful tool for estimating energy expenditure and tracking physical activity.
Heart Rate Monitors
A heart rate monitor can help measure calories burned during a workout by using the heart rate as an indicator of the intensity of the exercise. When you exercise, your heart rate increases, and the higher your heart rate, the more calories you burn.
Heart rate monitors use sensors to measure your heart rate during exercise and then use algorithms to estimate the number of calories burned based on your heart rate and other factors such as age, gender, weight, and fitness level.
It's important to note that heart rate monitors may not be completely accurate in estimating calorie burn, as individual factors such as metabolism and body composition can affect energy expenditure. Research shows that when investing in a heart rate monitor, chest strap monitors are more accurate than other wearables. 
Workouts that Burn the Most Calories
As previously reviewed, there are many factors that contribute to the number of calories burned in a particular workout. However, generally speaking, the following types of workouts are known to burn the most calories:
- High-Intensity Interval Training (HIIT): HIIT workouts involve short bursts of intense exercise followed by periods of rest or low-intensity exercise. This type of workout is known to be very effective in burning calories in a short amount of time.
- Running and Jogging: Running and jogging are both high-impact cardiovascular exercises that can help burn a significant amount of calories. The exact number of calories burned will depend on factors such as speed, duration, and incline.
- Cycling: Cycling is a low-impact cardiovascular exercise that can help burn a lot of calories. Like running, the number of calories burned will depend on factors such as speed, duration, and resistance level.
- Swimming: Swimming is a full-body workout that can help burn a lot of calories while also being low-impact and easy on the joints. The exact number of calories burned will depend on factors such as stroke type, speed, and duration.
- Rowing: Rowing is a full-body workout that engages both the upper and lower body muscles. It is known to be a very effective calorie-burning exercise, especially when performed at high intensities.
- Jumping Rope: Jumping rope is a simple yet effective cardiovascular exercise that can help burn a lot of calories. It is also very convenient as it can be done almost anywhere with minimal equipment.
How Long Should You Work Out to Lose Weight?
The amount of time you should work out to lose weight depends on various factors such as your current weight, fitness level, and the intensity of your workouts. However, as a general guideline, the American College of Sports Medicine recommends that adults engage in at least 150 minutes of moderate-intensity aerobic exercise or 75 minutes of vigorous-intensity aerobic exercise per week to maintain overall health.
To lose weight, you may need to increase the amount of time you spend exercising or the intensity of your workouts. Depending on your weight loss goals, you may need to engage in 300 minutes or more of moderate-intensity exercise per week.
It's also important to incorporate strength training exercises into your workout routine to build lean muscle mass, which can help increase your metabolism and aid in weight loss.
It's important to note that weight loss is not just about exercise, but also about maintaining a healthy diet and making lifestyle changes such as getting enough sleep and managing stress. A combination of regular exercise and healthy habits is the most effective way to achieve and maintain weight loss over the long term.
Calories Aren’t Everything
Measuring caloric burn and intake can be a very useful tool when trying to add or lose weight with a standard energy balance equation. However, calories truly aren’t everything. Other factors of health and fitness such as strength, posture, balance, mobility are just as important (if not much more) than aesthetics. The big takeaway? Find various forms of movement and exercise that you love and create a fitness routine that is enjoyable and maintainable for the long term.
- Ainsworth, Barbara E et al. “2011 Compendium of Physical Activities: a second update of codes and MET values.” Medicine and science in sports and exercise vol. 43,8 (2011): 1575-81. doi:10.1249/MSS.0b013e31821ece12
- Gillinov, Stephen et al. “Variable Accuracy of Wearable Heart Rate Monitors during Aerobic Exercise.” Medicine and science in sports and exercise vol. 49,8 (2017): 1697-1703. doi:10.1249/MSS.0000000000001284