I am having trouble converting a recipe from metric to US: 50 g butter, 100 ml cream, 100 g chocolate, 150 g blackberries.

I use a few different methods for converting metric to Imperial.

1. Guesstimate. One pound = 454 grams, so 100g chocolate is about four ounces, etc.
2. One ounce = 28.35 grams.
3. Google or I love the app Smart Chef for conversions
4. Most liquids are listed as ml as well as ounces
5. A $30 digital scale can toggle between grams and ounces - it's great to see what grams "look like."

I will plug metric here. Cups and ounces do not help people bake better. it's so easy to add or remove 10% of 100, than 1/3C. As well, 1/3C of sugar does not weigh the same as 1/3C of flour, etc. Seeing that all recipes are really ratios helps cooks expand beyond "the recipe" into spontaneous, inventive territories.

Sorry, I'm off my metric soap box now.

Some people print a conversion chart and post it conveniently in the kitchen, or near a desk.
After a while, you can move easily between metric and US or Imperial, even without a scale (which is, of course, a useful thing to have around).
For example,
http://startcooking.com/measurement-and-conversion-charts

Use SIRI on your cell phone and get an instant answer!

kl, i simply go to google and type in, for instance:
"50 gms= ounces" or "100 ml= ounces"and I get what i need. Try that.

To translate grams to ounces, multiply by 0.035.
To convert a milliliter to an ounce, multiply the milliliter by 0.034.
To translate centimeters to inches, multiply the centimeter by 0.39.

Source: Fannie Farmer Cookbook, 1979 edition

If your calculator batteries are dead or you've misplaced your smartphone, just have Google do this for you. Here's the page if you type in "grams ounces" into the search parameters at www.google.com:

https://www.google.com/?gws_rd=ssl#q=grams+ounces

Good luck.