Not a tool at all
This is a quote from a reply from Jim the Admin posted in a earlier discussion:
"Hi Everyone. Great suggestions. Sometimes getting the correct calorie burned information for activities can be hard. Vendors aren't always the most reliable sources and studies that contain all the info are a bit hard to come by.
We would love to do custom activity functionality, but it isn't quite as easy as custom foods. Where foods have a certain nutrition for everyone who eats it, activities don't work that way. Usually calorie burn is determined by a percentage of your normal metabolism. So, for example, doing some hard work might burn 200% of you normal metabolism. Most users won't have this kind of information to create the custom activity. You can't just enter 200 calories/hr because that will change as your weight and metabolism change. We will think about it though and see if we can simplify and get something to you.
Also, keep up the suggestions for which activites to add to our database. I will do special searches for these activities and try to find some studies with good data.
Thanks again! We love the suggestions.
Since I have a fair bit of access to data regarding calories burned for my body, I usually find a similar activity in the drop-down and modify the times, distance, or reps until it matches what my data says. Not perfect and a little tricky for weights, but is seems to work OK for may aerobic activities.