Flounder: Nutrition, Flounder vs Sole and Is Flounder Healthy?

Flounder is a thin, delicate flatfish with a mild flavor and fine flakes, and it is the lowest-calorie fish in this guide’s USDA comparison. A 3-ounce portion of cooked flounder and sole has about 73 calories, 13 grams of protein and 2 grams of fat. This guide covers flounder nutrition per serving, how flounder vs sole compare at the fish counter, what fluke is, why the sodium number deserves a look, and where flounder sits in the FDA mercury chart, so you can decide whether flounder is healthy for your kitchen.

Peptide Labs does not sell fish or seafood products. This article is general nutrition information, not medical advice. For a firmer, higher-protein white fish, see our sibling red snapper guide.

What is flounder?

Flounder is a common name for several flatfish. They swim on one side, and as adults both eyes sit on the upper side of the body. NOAA Fisheries describes summer flounder (Paralichthys dentatus) as a left-eyed flatfish, with both eyes on the left side when viewed from above. Its other names include fluke and northern fluke. It lives in the Atlantic from Nova Scotia to the east coast of Florida and is most common from Cape Cod to Cape Fear, North Carolina.

NOAA reports that the summer flounder stock is not overfished and not subject to overfishing, and describes the meat as delicately flavored with a flaky, fine texture. Winter flounder and other species are sold too, and frozen fillets may simply say flounder. FDA’s allergen guidance notes that a label’s “Contains” statement may give a general name such as “flounder” for a specific species, while the ingredient list uses the accepted market name.

Flounder nutrition per serving (USDA)

USDA FoodData Central SR Legacy groups these fish into a single entry, flatfish (flounder and sole species), so there is no flounder-only value. The table shows that entry for a 3-ounce (85 g) portion cooked by dry heat, with percent Daily Value (%DV) based on FDA Daily Values.

A whole cooked fillet in the same USDA entry weighs 127 g and has about 109 calories and 19.4 g of protein. Raw, the entry (FDC 174196) lists 70 calories and 12.4 g of protein per 100 g. Flounder is mostly water, which is why the calorie and protein numbers per ounce are lower than for firmer fish such as snapper or tilapia.

Among the minerals, selenium and phosphorus stand out, and the fish carries a modest amount of vitamin D and choline. More on these nutrients: selenium, B12 foods and high-protein foods.

A note on sodium

The USDA flatfish entry lists 309 milligrams of sodium per 3 ounces cooked, or 13% of the Daily Value, against 49 milligrams for snapper and 48 milligrams for tilapia in USDA data. A whole cooked fillet reaches 461 milligrams, 20% of the FDA Daily Value. Products differ, so if sodium matters to you, compare the Nutrition Facts labels on packaged fillets and see our guide to low-sodium foods.

Flounder vs sole: what is the difference?

At the fish counter, flounder vs sole is more about names than nutrition. Both are flatfish with thin, mild, quick-cooking fillets, and USDA does not separate them in its standard reference data. The FDA and EPA fish chart also lists flounder, sole and plaice side by side in the same lowest-mercury group. In recipes they swap freely: pan-fried, baked with lemon, rolled around a filling or used for fish tacos.

• Nutrition: one shared USDA entry, so no reliable difference to report.
• Mercury: same FDA and EPA group for flounder, sole and plaice.
• Labels: the market name on the package tells you the species; the Contains line may show a broader name.
• Fluke: another name for summer flounder, according to NOAA, which also lists northern fluke and hirame as names for the same fish.

How flounder compares with other fish

Flounder is the lightest fish in this comparison by calories and protein per portion. Its omega-3 EPA and DHA content is similar to snapper’s and well below that of fatty fish such as sardines or trout. Our omega-3 guide explains why that matters to some readers.

For tilapia in detail, see our tilapia guide. Flounder’s cholesterol is moderate for fish; our foods high in cholesterol guide puts that number in context.

Is flounder healthy? Mercury, allergy and cooking

• Mercury: the FDA and EPA fish chart, written for people who might become or are pregnant or breastfeeding and for children ages 1 to 11, lists flounder in its lowest-mercury group. Ask your clinician how often fish fits your situation; we do not repeat serving amounts here.
• Allergy: FDA names flounder among its examples of bony fish, which are a major food allergen. Fish allergy is separate from shellfish allergy; an allergist can tell you which foods to avoid.
• Cooking: FoodSafety.gov advises cooking fin fish to 145 F, or until the flesh is opaque and separates easily with a fork. Thin flounder fillets cook in minutes, so they dry out quickly.
• Preparation: breading, frying and butter sauces add far more calories and fat than the fish itself.

Flounder works well in a pescatarian diet for people who want a mild fish that even fish-shy eaters accept. So, is flounder healthy? On nutrition it is very lean, low in calories and rich in selenium and B12, with a place in the lowest-mercury group; the main things to watch are sodium in some products, the allergen status of all fish, and what the cooking method adds.

Frequently Asked Questions

Questions about a label? Contact us or read our Buyer’s Guide. Food comes first; follow the label and ask a healthcare provider before starting a supplement, especially if you take medicines, are pregnant or have a food allergy. These statements have not been evaluated by the Food and Drug Administration. This product is not intended to diagnose, treat, cure, or prevent any disease.

Last reviewed October 2026.

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