We have a converter that will convert any imperial measurement to metric when you add a food to your tracker--that is the conversion calculator Unident was referring to. You can convert grams to ounces, pounds, etc., via that calculator.
I am not sure what you mean by a "gram to calorie" converter, as there is not a standard conversion for that. One gram of a particular food may have more or less calories than one gram of another food (for example, grams of oil vs. grams of celery). If that isn't what you mean, can you describe what you mean by converting grams to calories?