To accurately take account of our gains and losses, it's best to use a device like a heart rate monitor, which can get an accurate reading by using electrical impulses. Without a heart rate monitor, there's not an accurate method with which you can find the precise numbers. While there are a wealth of online logs of the calories expended doing a range of activities, these are merely estimates. They can be off by quite large margins because we are all different and are starting at out on our own unique fitness levels.
You can find a wide range of heart rate sports watches from HeartRateMonitorsUSA.com. There are different brands like Garmin and Polar, which are quite popular among fitness enthusiasts. Ultimately, your choice comes down to what you find necessary for you. Some of the most high-end models feature a great deal of extra features that you probably won't need. If you feel like making the extra investment, you may as well go for a model that's strap-less.