Because different people have different jobs and different levels of activity, it is not possible to come up with an exact formula for caloric requirements.

Fromm a practical viewpoint, you can do a reasonable estimate. The usual approach is to separate the requirement into:
1- Basal Metabolic Rate (BMR) - This is the number of calories you need to just keep you alive and well. No consideration is given for any physical activity. It is approximately what you would need if you slept all day. There are a few different formulae around that are reasonably accurate. Google BMR and you will find some calculators and the formulae. They take into consideration your age, gender and body composition. This represents the majority of your daily consumption and there is little you can do to alter this number.

2- The thermic effect of food. This is the number of calories you burn digesting your food. Some foods are more costly than others to burn but generally 10% of your BMR is approximately correct.

3- Your activity level. This portion can be divided up into an estimate of your general daily activity and an estimate of your defined activity (running). A sedentary person might burn 20% of the above total in general activity. Such a person might be a unemployed person who generally watches TV all day. A very active person might burn 50% of the above total. Such a person might be a construction worker doing fairly heavy physical work for much of the work day. These numbers are estimates and you must use your best judgement of your own activity level to come up with an appropriate number for you. Your defined exercise activity (running) can be more accurately tracked. For someone your size, 100 calories per mile is likely very close. Possibly. you might burn 110 per mile but the usual estimate is around 100.



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gotta run...