MINNEAPOLIS (WCCO) – When we hit the treadmill, it makes us feel good to see how many calories we’re burning.

“If I’m on 60 minutes, it’s about 1,000 calories. Not bad.” said one Lifetime Fitness member.

But some take burning off a brownie in 30 minutes with a grain of salt.

“The information that you’ll put into a treadmill doesn’t ask you a whole heck of a lot,” said Lifetime Fitness personal trainer Sarah Hankel. “The more information you have, the more accurate the number is going to be.”

Hankel says, on average, some of the machines overestimate calories burned by between 200-300 an hour.

“Think about it,” Hankel said. “Every single person has a different fitness ability level.”

How many calories you burn depends not just on your weight, but on your percentage of lean muscle, fitness level and how hard your heart is working, Hankel said. She recommends a heart rate monitor and a fitness test to measure how much oxygen circulates through your system when you exercise.

Exercise companies say their machines are fairly accurate and can fluctuate between 4 and 15 percent based on a person’s metabolism and biomechanical efficiency.

According to Bob Star, head of interactive health at Lifespan, it’s the most accurate indirect measure available, especially for treadmills that have been highly tested. Most companies based their numbers on standards set by American College of Sports Medicine.

Hankel says one shouldn’t ignore the number on the machine, but rather use it as a ballpark and include more research about your own body to get a more accurate picture of how many calories you’re burning.