A common formula for approximating calorific expenditure is:

Kcal/Min ~= 5 * massKg * VO2 / 1000

Where: the VO2 is the volume of Oxygen consumed (mL/Kg/min), this variable can be guestimated based on your heart rate in a given period e.g.

VO2 = (currentHeartRate / MaxHeartRate) * VO2Max

where:

MaxHeartRate ~= 210 - (0.8 * ageYears)

VO2Max ~= 15.3 * (MaxHeartRate / BasalHeartRate)

A common formula for approximating calorific expenditure is:

Kcal/Min ~= 5 calories * massKg * VO2 / 1000

Where:

• The 5 calories/min constant assumes you're primarily burning carbohydrates over a short period, while awake, if the exercise is sustained for a period use 4.86 to reflect a mix of fat and carbohydrates are being converted to energy.
• the VO2 value is the volume of Oxygen consumed (mL/Kg/min), this variable can be guestimated based on your heart rate in a given period e.g.

VO2 = (currentHeartRate / MaxHeartRate) * VO2Max

where:

MaxHeartRate ~= 210 - (0.8 * ageYears)

VO2Max ~= 15.3 * (MaxHeartRate / BasalHeartRate)