A medium raw tomato (about 123 grams) contains roughly 4.8 grams of total carbohydrates. That’s low enough to fit comfortably into most eating plans, including low-carb and keto diets. But the number shifts depending on the type of tomato, how it’s prepared, and whether you’re eating it fresh or from a can.
Carbs by Tomato Type and Size
Not all tomatoes land at the same number. A cup of cherry tomatoes (149 grams) comes in at about 5.8 grams of carbs, slightly more than a single medium tomato simply because you’re eating a bit more fruit by weight. Larger beefsteak or heirloom varieties will scale up proportionally, but the carb density stays consistent at around 3.9 grams per 100 grams of raw tomato.
Roma tomatoes, often called plum tomatoes, tend to be meatier with less water and slightly more concentrated sugars. Grape and cherry tomatoes also taste sweeter than slicing varieties, though the actual difference in carbs per gram is small. If you’re closely tracking macros, weighing your tomatoes on a kitchen scale gives you a more accurate count than estimating by size.
What Makes Up Those Carbs
Most of the carbohydrate in a tomato comes from simple sugars, primarily glucose and fructose in nearly equal amounts. Sucrose is barely present, typically less than 0.1% of the fruit. The rest of the carb content is dietary fiber, with a medium tomato providing about 1.5 grams. Subtract that fiber and you get roughly 3.3 grams of net carbs per medium tomato.
That fiber is mostly insoluble, made up of cellulose, hemicellulose, and lignin concentrated in the skin and seeds. A smaller portion is soluble fiber, mainly pectin. The insoluble fiber supports regularity and digestive function, while the soluble pectin fraction plays a role in blood sugar and cholesterol management. Eating the skin gives you the most fiber benefit.
How Cooking Changes the Numbers
Raw tomatoes have the highest water content. When you cook them, some of that water evaporates, which concentrates everything left behind, including carbohydrates. Cup for cup, cooked tomatoes contain more carbs than raw ones simply because you’re packing more tomato into the same volume.
Tomato paste is the most extreme example. A quarter cup (66 grams) of canned tomato paste contains 12.5 grams of carbs. That’s because paste is made by cooking tomatoes down to a thick concentrate, removing most of the water. Canned diced or crushed tomatoes fall somewhere between raw and paste, depending on how much liquid is in the can. If you’re using tomato-based sauces, the added sugars in many commercial brands can push the carb count higher than the tomatoes alone would suggest, so checking the label matters.
On the nutrition side, cooking does unlock more lycopene, the pigment that gives tomatoes their red color. One cup of cooked tomatoes delivers about 7,300 micrograms of lycopene compared to roughly 4,600 in raw, because heat breaks down cell walls and makes it easier to absorb. So while cooking concentrates carbs, it also concentrates beneficial compounds.
Tomatoes on a Low-Carb or Keto Diet
With only about 3.3 net carbs per medium tomato, fresh tomatoes are one of the more keto-friendly fruits. A standard keto diet limits daily carbs to 20 to 50 grams, so a whole tomato in a salad or a few slices on a burger uses a small fraction of that budget. Cherry tomatoes in a handful as a snack stay well within range too.
Where low-carb dieters run into trouble is with concentrated tomato products. A quarter cup of tomato paste in a recipe adds 12.5 grams of carbs before you account for anything else in the dish. Tomato-based soups, sauces, and ketchup can add up quickly. Sticking with fresh or lightly cooked tomatoes keeps the carb impact minimal.
Glycemic Impact
Tomatoes have a low glycemic index, falling below 55 on the standard scale. Their glycemic load, which accounts for how many carbs you actually eat in a typical serving, is even less of a concern. The combination of low total carbs, a roughly equal glucose-to-fructose ratio, and a decent amount of fiber means tomatoes produce a gentle, gradual blood sugar response rather than a spike. For people managing blood sugar, tomatoes are one of the least problematic foods in the produce aisle.
Quick Carb Reference
- 1 medium raw tomato (123g): 4.8g total carbs, ~3.3g net carbs
- 1 cup cherry tomatoes (149g): 5.8g total carbs
- 1/4 cup tomato paste (66g): 12.5g total carbs
- 1 thick slice of tomato (~27g): ~1g total carbs