You're standing in the grocery aisle, staring at a wall of silver and blue labels. You grab a can, thinking it’s the same size your mom used for casserole back in the 90s. It isn’t. Not even close. If you’ve ever wondered how many ounces in tuna can actually remain once you peel back that lid, you aren't alone. Most of us just assume a "standard" size exists, but the industry has been quietly shaving off fractions of an ounce for decades.
It’s frustrating.
Standardization in the tuna industry is basically a myth these days. While you might expect a solid 6 ounces, what you’re likely holding is a 5-ounce or even a 4.5-ounce container. And that's before we even talk about the "drained weight," which is the only number that really matters when you’re trying to figure out if you have enough protein for a decent sandwich.
The 5-Ounce Standard and Why It’s Disappearing
For a long time, the 6-ounce can was king. It was the gold standard for brands like Starkist, Bumble Bee, and Chicken of the Sea. Then, around 2008, a massive shift happened. Costs went up, and instead of raising prices to a level that would scare off shoppers, the big three tuna processors dropped the volume. They moved to the 5-ounce can.
People noticed, but not enough to stop buying.
Today, if you check the shelf at a Kroger or a Walmart, the most common answer to how many ounces in tuna can is 5 ounces (142 grams). However, "shrinkflation" is a persistent beast. Some premium brands or store-brand "budget" cans have started creeping down to 4.5 ounces or even 4 ounces. You’re paying roughly the same price—or more—for less fish.
It’s a classic bait-and-switch.
When you look at the label, that 5-ounce figure represents the "net weight." That includes the fish, the water, the oil, or whatever broth they’ve shoved in there to keep the meat moist. If you’re a stickler for macros or you’re following a strict recipe, that number is incredibly deceptive. Once you press that lid down and squeeze out the liquid, you’re often left with only 3 to 3.5 ounces of actual tuna.
Understanding Net Weight vs. Drained Weight
Let’s get technical for a second because the FDA has some very specific thoughts on this. The "Net Weight" printed on the front of the can is the total weight of the contents. But the "Drained Weight" is what’s left after you get rid of the packing medium.
If you buy tuna in oil, the oil is heavy.
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If you buy it in water, the water is absorbed into the fibers of the fish.
According to the National Oceanic and Atmospheric Administration (NOAA) and FDA standards, canned tuna must meet a minimum "press weight" to ensure consumers aren't just buying a can of saltwater. For a standard 5-ounce can, the expected drained weight usually hovers around 3.25 to 4 ounces. If you get a can that feels particularly "sloshy," you're likely getting the bare minimum of protein.
The Rise of the Tuna Pouch
Recently, the industry has pushed the pouch. You’ve seen them—the colorful, tear-open bags that don't require a can opener. These are usually 2.5 ounces or 2.6 ounces.
Why the weird number?
Because pouches don't require the extra "packing liquid" to stay fresh in the same way cans do. A 2.6-ounce pouch often contains nearly as much actual meat as a 5-ounce can once the can has been drained. It’s more expensive per ounce, sure, but you’re paying for the convenience of not having to stand over the sink like a chemist trying to squeeze out every drop of brine.
Does the Species of Tuna Change the Weight?
Honestly, yes. Sorta.
Skipjack is the most common tuna you’ll find in those "Chunk Light" cans. It’s smaller, softer, and holds more water. When you drain a can of skipjack, it tends to lose more volume because the meat is fragmented. Albacore, or "Solid White" tuna, is different. It’s denser. It’s firm.
If you open a 5-ounce can of Solid White Albacore, you’ll usually find a single "plug" of fish. Because the muscle fibers are larger and tougher, they don’t hold onto as much excess water. You end up with a higher "yield" of edible fish compared to the mushy skipjack.
Then there’s the luxury stuff.
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Brands like Tonnino or Ortiz often sell tuna in glass jars. These are frequently 6.3 ounces or 7 ounces. These brands focus on "Ventresca" (tuna belly) or solid fillets packed in high-quality olive oil. In these cases, you actually want the weight of the oil because it’s part of the culinary experience, not just a filler to make the can feel heavy on the grocery shelf.
The Lawsuits Nobody Talks About
The tuna industry hasn't exactly been a paragon of transparency. In the mid-2010s, there were massive class-action lawsuits targeting the major brands. The allegation? They were under-filling cans. Testing showed that some "5-ounce" cans contained significantly less than the required amount of fish.
One notable case involved StarKist. They eventually settled for millions, offering consumers either a small cash payment or—get this—more tuna. It highlighted a reality that most shoppers ignore: the numbers on the can are more like "guidelines" to the manufacturers than a sacred vow.
You should always look for the "Non-GMO Project Verified" or "MSC Certified" labels, but even those won't tell you if the factory had a "light fill" day.
How to Calculate What You Actually Need
If a recipe calls for "two cans of tuna," it’s probably assuming the old-school 6-ounce standard. If you use two of today’s 5-ounce cans, your tuna salad is going to be dry or skimpy. You're missing 2 ounces of total weight, which is about a quarter of a serving.
To get it right, you have to do a little "grocery store math."
- For a party size bowl: You likely need three 5-ounce cans to match what used to be two large cans.
- For a single sandwich: One 5-ounce can (drained) is perfect.
- For high-protein diets: Aim for the 7-ounce "Jumbo" cans if you can find them, though they are becoming increasingly rare in standard supermarkets.
Beyond the Can: Large Format Tuna
If you’re prepping for a big event or just a really long winter, you’ll see the "food service" size. This is the massive 66.5-ounce tin, often called a "Size 10" can.
Don't buy this unless you have a plan.
Once opened, tuna has a very short shelf life. Even if it’s submerged in liquid in the fridge, it starts to oxidize and pick up a "tinny" flavor within 48 hours. The weight advantage of the 66.5-ounce can is huge—it’s much cheaper per ounce—but the waste factor for a normal household is massive.
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Actionable Steps for the Savvy Shopper
Don't let the label trick you. The next time you're stocking the pantry, keep these points in mind to make sure you're actually getting your money's worth.
Check the Net Weight every single time. Brands often change can sizes without changing the packaging dimensions. They just make the "puck" at the bottom of the can deeper so the container looks the same height while holding 0.5 ounces less. It’s a psychological trick called "slack fill."
Prioritize pouches for travel or work. If you don't want to deal with draining liquid, the 2.6-ounce pouch is the most honest measurement of fish you can buy. What you see is what you get.
Look at the "Price Per Ounce" on the shelf tag. Most grocery stores are required to list this. Ignore the $1.50 or $2.00 price tag and look at the tiny number in the corner of the label. That's the only way to compare a 5-ounce can to a 4.5-ounce can fairly.
Opt for Albacore if you want more meat. Because Albacore is denser, you generally get more "fish" and less "mush" after draining. It’s worth the extra 50 cents if you’re looking for texture.
Drain properly but don't overdo it. If you squeeze the tuna until it’s a dry, white powder, you’re losing flavor and nutrients like Omega-3 fatty acids. A gentle press with the lid is enough.
Knowing how many ounces in tuna can is just the start. The real skill is recognizing that the number on the front is a starting point, not the final result. Be skeptical of the packaging, watch for shrinkflation, and always buy based on the drained protein you actually need for your meal.
The era of the 6-ounce can is over, and the 5-ounce can is already on life support. Pay attention to those labels, or you'll keep paying more for a lot of salt water and very little fish.