Cycling is an aerobic activity that burns calories. Unfortunately there is no direct way to measure this.

KJ's of work completed can be a reasonable 1:1 approximation of calories burned. KJ (work) can be quantified with a power meter.

On one side, the calorie to joule ratio is ~1:4, so there are four joules per calorie. On the flip side, the body is only about ~25% or so efficient in producing exercise related work, losing the other 75% of energy produced as heat. These effects tend to cancel each other out, and the net effect is that KJ's of work done is similar to calories burned during aerobic exercise.