A whole raw cucumber (about 8 inches long) contains roughly 11 grams of carbohydrates. That’s remarkably low for a food its size, and the reason is simple: cucumbers are about 96% water, giving them one of the lowest carbohydrate densities of any vegetable.
Carbs by Serving Size
Most people don’t eat a whole cucumber in one sitting, so here’s how the carbs break down across common portions:
- One whole cucumber (301 g): 11 g total carbs, 1.5–2 g fiber, 5 g sugar
- One cup sliced, with skin (about 119 g): roughly 4 g total carbs
- One cup sliced, peeled (about 119 g): about 2.6 g total carbs, 0.8 g fiber
The skin accounts for a meaningful share of both the fiber and total carbs. Peeling a cucumber cuts the carbohydrate content by about a third per cup, though you also lose some of the fiber that slows digestion.
Net Carbs for Keto and Low-Carb Diets
If you’re tracking net carbs (total carbs minus fiber), one cup of sliced cucumber with the skin on comes to about 3 grams of net carbs and just 16 calories. That makes cucumbers one of the most keto-friendly vegetables available. For context, the typical keto daily limit is 20 to 50 grams of net carbs, so you could eat several cups of cucumber without making a dent in your allowance.
Sugar Content
A whole cucumber contains about 5 grams of sugar, split between fructose, glucose, and a small amount of sucrose. Nearly all of it is “reducing sugar,” meaning fructose and glucose rather than sucrose. The total sugar concentration of the fruit stays below 3% by weight, which is why cucumbers taste mild and refreshing rather than sweet.
Glycemic Impact
Cucumbers have a glycemic index of 15, which is very low. For comparison, white bread scores around 75, and even carrots land near 40. The combination of high water content, low sugar, and moderate fiber means cucumbers cause almost no measurable spike in blood sugar. Their glycemic load, which factors in the small amount of carbs per serving, is close to zero.
Why Cucumbers Are So Low in Carbs
The 96% water content is the main explanation. When a food is almost entirely water by weight, there simply isn’t much room left for carbohydrates, protein, or fat. A whole cucumber weighs about 300 grams but delivers only 11 grams of carbs and around 45 calories. By contrast, 300 grams of potato would contain roughly 50 grams of carbs. That water density also makes cucumbers useful for staying hydrated, particularly in warmer months or alongside salty meals.
Peeled vs. Unpeeled
Leaving the skin on adds a small amount of carbohydrate but also boosts fiber, which offsets the difference if you’re counting net carbs. The skin is also where most of the cucumber’s vitamins concentrate. Unless you have a specific reason to peel (texture preference, waxed skin, or digestive sensitivity), keeping the skin gives you a better nutritional return for roughly the same net carb count.