Did you ever wonder how many calories you use while cycling?  Here is a table to help you figure it out!  These numbers are from Cycling, 1989 issue.  It assumes flat terrain, no wind, upright position!  The second table is the same, but gives calories per mile, and the third table is based on heart rate.
 Speed MPH 12 14 15 16 17 18 19 Weight lbs CALORIES PER HOUR 110 293 348 404 448 509 586 662 120 315 375 437 484 550 634 718 130 338 402 469 521 592 683 773 140 360 430 502 557 633 731 828 150 383 457 534 593 675 779 883 160 405 485 567 629 717 828 938 170 427 512 599 666 758 876 993 180 450 540 632 702 800 925 1048 190 472 567 664 738 841 973 1104 200 495 595 697 774 883 1021 1159
 Speed MPH 12 14 15 16 17 18 19 Weight lbs CALORIES PER MILE 110 24.42 24.86 26.93 28.00 29.94 32.56 34.84 120 26.25 26.79 29.13 30.25 32.35 35.22 37.79 130 28.12 28.71 31.27 32.56 34.82 37.94 40.68 140 30.00 30.71 33.47 34.81 37.24 40.61 43.58 150 31.92 32.64 35.60 37.06 39.71 43.28 46.47 160 33.75 34.64 37.80 39.31 42.18 46.00 49.37 170 35.58 36.57 39.93 41.63 44.59 48.67 52.26 180 37.50 38.57 42.13 43.88 47.06 51.39 55.16 190 39.33 40.50 44.27 46.13 49.47 54.06 58.11 200 41.25 42.50 46.47 48.38 51.94 56.72 61.00

Another "fairly" accurate way to figure calories used per minute is the graph on left.  If your heart rate is sustained at a certain rate, you can read on the graph the calories used per minute.  (I do not recall the origin of this graph, hence I am unable to give credit to its author.)

 The PPTC main web-page can be reached at the PPTC Web Site.