Converting US standard measurements to metric

At https://convertrecipe.com you can convert the whole recipe from US to metric or from metric to US with just one click.

I will just add a few more idea to the above. Develop your recipes. Once you have gone through the conversion process, you will know how your ingredients behave i.e. how much the flour you use weighs per cup. If your language skills are good, use original recipes. The Internet is great for this purpose. Do not get too hung up on precision. Conversion tables are for scientists or analysts and as cooks we can use a lot more discretion.

Measuring flour by volume is problematic hence you will find a considerable variation converting cups to weight. Some recipes are based on (the most accurate method) sometimes referred to as "scoop and sweep", some bakers don't bother striking off the measuring cup, some sift before measuring, some pack the flour into the cup as if it were brown sugar. None of this is ever mentioned in the recipe but you have to start somewhere. I use the aforementioned 5 oz. / cup then make adjustments if necessary.

If you are baking, I would suggest using weight rather than volume. Dry ingredients such as flour can vary drastically depending upon how "settled" the ingredient is at the time of measurement.

Your best bet is to buy a digital scale for the kitchen which has both metric and US standard settings then you do not even have to worry about conversions.

Thanks all. I guess my only concern with using Google is that there seems to be a great disparity of answers given in the websites. For instance, ChefOno says that 1 cup ap flour is 140 grams. I trust his measurement. But I soon found another site saying that 1 cup ap flour is 125 grams. That's quite a big difference.
Also, it's true that many cookbooks have basic conversion tables in the back. I'm looking at one right now. The problem is that all it tells me is that 1 ounce equals 28.35 grams. This is not terribly helpful for figuring out how many grams are equal to a cup of ap flour.
However, WileyP has created an amazing table that should help quite a bit. Thanks so much for your answers, everyone!

Google provides the easiest answer for me. As Chef Ono said, all you have to do is enter your question, say "150 g in oz" or "1 c in ml", and either the answer pops up or you get a list of websites that will answer the question. This works for temperature, distances, all sorts of measurements.

Most general purpose cookbooks have a conversion table in the back.

I have developed a MS Excel spreadsheet with weights in lb/oz and g/kg for various baking ingredients in quantities from 1 teaspoon through 5 cups. the spreadsheet covers such items as AP flour (both un-sifted and sifted), bread flour (both un-sifted and sifted), cake flour (both sifted and un-sifted), whole wheat flour, dark rye flour, granulated white sugar, both light and dark brown sugar, etc. If you PM me with your e-mail, I'd be happy to send it along to you.

For many packaged ingredients, the nutrition label has the conversion. For instance, on the bag of King Arthur White Whole Wheat Flour, 1/4 cup = 30 g; 1 cup = 120 g. The Metric Kitchen, www.jsward.com/cooking/conversion.shtml has tables, including one for commonly used foods.

I use the "Convert Units" iPhone app (free!). Doesn't answer things like how much does 1 cup of AP flour weigh in grams, but it is generally very helpful! I search internet for specific thing like that former question.

Google will do the math by entering "X oz to gr".
I convert AP flour at 140 gr / cup.

There are plenty of useful apps available. I have one on my iPad which digs me out of any conversion cooking problems I encounter. I love buying and cooking from cookbooks from all over the world. My app has been absolutely great!