The Power to Weight Ratio (PWR) is your power output divided by the rider weight in kilograms. A recreational cyclist might have a PWR of 2.5, 2.1, 1.8 for 5, 20, and 60 minutes of sustained activity respectively.

The energy expenditure was calculated using an efficiency 0%. It uses the formula taken from:

Ettema, G., & Lorås, H. W. (2009). Efficiency in cycling: a review. European Journal of Applied Physiology, 106(1), 1–14. doi:10.1007/s00421-009-1008-7

The efficiency is a function of both cadence (here taken to be 80 rpm) and external power.