To calculate your weight in kg, divide your weight in pounds by 2.2. So, if you weigh 165 pounds, which is 75 kilograms, 1 minute of performing crunches with moderate effort will burn (3.8 × 3.5 × 75) / 200 which equals 4.9 calories. An average person performs 30 crunches in a minute, burning around 5 calories .