White Zinfandel and blush wines in general are a commonly enjoyed wine style. These fresh, fruity, pink wines can go nicely with many meals.
The reason that many people enjoy white zinfandel wines is that they are very sweet. Of course, this sweetness comes from the natural sugars found in the grapes. Unfortunately for low carbers, sweet grape sugars are just like any other kind of sugar. They turn into fat cells in your body :)
Before I give some counts, it's important to realize why they vary. There is no such thing as a "white zinfandel grape". White zinfandel is a created product. They begin with a red zinfandel grape. They squish the grapes and let them sit for a short period of time, so only a bit of the red color comes off the grape skins. Then they let the pink liquid ferment. They specifically aim the winemaking to have a very sweet product.
As you can see, this is a very individual process that each winemaker does differently. There is no "one way" to make a white zinfandel. Some winemakers let it sit for a while. Some ferment quickly. Some cool ferment. All of these choices mean that different white zins end up with different carb counts.
Here are some numbers that I found. If your wine isn't listed, you can probably assume that it is somewhere in this range.
Almaden White Zinfandel - 6.8g / 4oz glass
Beringer White Zinfandel - 4.0g / 4oz glass
Sutter Home White Zinfandel - 6.4g / 4oz glass
Lisa Shea's Library of Low Carb Books