I use the info off the supermarket packaging when available, it's pretty accurate. Use the info on the back under Nutrition, not the summary on the front. Otherwise I use the Fat Secret website, which is UK based. You have to be careful with US sites as they measure things a bit differently, including fibre within carbs for one thing. Also, their portion sizes are a bit odd (when given) and they prefer to do things by portion rather than per 100g.