This is a SWAG for calories burned cycling 12-15mph:

* Divide your feet climbed by 10.
* Divide again by your average MPH.
* Add that to your total miles.
* Multiply the new number by the weight in pounds of you, your bike, and everything you’re carrying.
* Multiply the new number by 0.105 (or divide by 9.5).
* (Use 0.115 or 8.7 if you only know your own naked wake-up weight.)
* That is pretty close to your calories burned for the ride.
* Baseline here is me, 6’5″, anywhere between 250 and 290 pounds plus bike weight (any bike).

BMR is not a part of this SWAG:

* BMR is how much you burn in 24 hours of sleeping.
* Most people are around 9kcal per pound per day.
* BMR and is not based on your activity level (see TDEE).
* BMR is based in your microcellular efficiency, and is influenced by hormones.
* If you are on severe caloric restriction, it goes down.
* Thyroid issues can affect this either way.
* Baseline here is me, at 285 pounds, and averaging 2550 kcal per day.

Faster speeds pick up exponentially more wind resistance.

* Twice the airspeed has four times the wind drag.
* Higher density altitude has proportionally less drag.
* Shorter and narrower shouldered people people have less wind drag.
* Fatter people are slightly more aerodynamic, so the increased wind profile is not THAT much of an issue.
* Cycling 10mph into a 5mph headwind has as much wind drag as cycling 20mph with a 5mph tailwind.
* 12-16mph is the 50% transition for wind vs other factors on flat ground. (13mph for me at 6 sqft)
* Baseline here is me, with about 6 square feet of frontal area, about 22 Watts at 10mph, and about 150 Watts at 20mph, just for wind.

Rolling resistance is a big part of drag.

* Increases linearly with speed (2x speed is 2x the rolling drag).
* Lower weight is better (because tiny bumps have to push you UP over them).
* Race tires can be half the CRR of average tires.
* Wider tires are better by around 1% per mm with 23mm as baseline.
* Baseline is me, at 310 total, 31W at 10mph, or 61W at 20mph on 1% grade.

Routes with less uphill than downhill will cost fewer calories.

* Increases linearly with speed (2x speed is 2x the gravity drag).
* 1% uphill is 2x the drag of rolling resistance. 2% is 4x.
* Lower weight people do way better on both gravity and CRR.
* Baseline is me, at 310 total, 62W at 10mph vs 124W at 20mph on 1% grade.

Good links:

* https://www.gribble.org/cycling/power_v_speed.html
* http://mccraw.co.uk/wind-resistance-cycling-speed/
* http://mccraw.co.uk/optimising-for-long-distance-speed/