The number of calories in a can of tuna depends on how it’s packed, in oil, brine, or spring water and the drained weight. A standard 145g can of tuna in brine or spring water (drained to about 112g) contains roughly 100 to 120 calories. In contrast, a can of tuna in sunflower oil or olive oil can contain 180 to 220 calories after draining, depending on how much oil is retained.

So, the calorie difference comes down to the oil even after draining, some oil is absorbed into the fish. Tuna in brine or spring water is significantly leaner than tuna in oil.

Nutritional Breakdown

Tuna is a high-protein, low-fat food when packed in water or brine. A typical drained can contains around 25 to 30 grams of protein, less than 1 gram of carbohydrate, and between 0.5 to 1.5 grams of fat, depending on the cut. When packed in oil, fat content increases to around 7 to 10 grams, which also raises the calorie total.

Tuna is rich in B vitamins, selenium, and omega-3 fatty acids (especially when packed in oil or from fattier cuts like yellowfin). It’s naturally gluten-free, low in carbs, and fits well into high-protein or low-calorie eating plans.

Tuna in Oil vs Brine vs Water

Tuna in oil delivers more flavour and richness but also more calories and fat. If you're trying to maximise protein with minimal calories, tuna in water or brine is the better choice. Brine-packed tuna has slightly more sodium than spring water varieties, but the calorie content remains low.

If you do prefer the taste of oil-packed tuna, draining it thoroughly or pressing it with a paper towel can remove some extra fat and reduce the calorie count by 20 to 40 calories.

How Tuna Supports Your Diet

Tuna is an excellent food for muscle building, fat loss, or general health. It’s high in protein, low in calories, and highly satiating, helping you feel full without a large portion size. It’s especially popular in meal prep and high-protein diets because it’s shelf-stable and requires no cooking.

A can of tuna with some wholegrain toast, salad, or vegetables creates a quick, balanced meal that typically stays under 400 calories in total, depending on extras like mayo or dressings.

Mercury Considerations

One thing to keep in mind with tuna is its mercury content. While safe in moderate amounts, it’s recommended to limit canned tuna to a few times per week, especially for pregnant individuals or young children. Light tuna (often skipjack) has lower mercury levels than white tuna (albacore), so that’s worth considering for frequent consumption.

Drained Weight vs Net Weight Can Be Confusing

One of the biggest sources of confusion with canned tuna is the difference between net weight and drained weight. A can might be labelled as 145g, but after draining, the actual edible tuna might be closer to 112g or even 90g, depending on how thoroughly it's drained. This matters because calorie counts are based on drained weight, not total can weight and if you don’t factor that in, your tracking could be off by 30–50 calories either way.

If you’re calorie counting, it’s best to weigh the drained tuna or check if the label includes a drained weight breakdown many brands do in small print.

Flavoured Tuna Can Be a Hidden Calorie Bomb

Tuna with added flavours such as sweet chilli, lemon pepper, tomato and basil, or teriyaki often seems like a convenient meal shortcut. But these varieties can carry extra sugars, oils, and preservatives that increase the calorie count. A flavoured 100g pouch that seems “lean” may contain 170–200 calories due to added sauces, compared to 100–120 calories in plain versions.

They’re not necessarily bad but should be treated more like a ready meal than a clean protein source if you’re watching calories closely.

Tuna Mayo Is a Whole Different Ball Game

Tuna on its own is lean, but as soon as you add mayonnaise, calorie content skyrockets. A standard tablespoon of full-fat mayo adds about 90–100 calories, and most people use two or three spoonfuls in a tuna sandwich or salad meaning 200+ extra calories. This turns a light protein into a 300–400 calorie meal base, even before bread or extras are added.

A good alternative is using low-fat Greek yoghurt, light mayo, or mustard to cut those calories in half or more, while keeping the texture and flavour.

Tuna Is Calorie-Efficient for High Protein Goals

From a macronutrient efficiency perspective, tuna is elite. A 112g drained can of tuna in water offers 25–30g of protein for just 100–120 calories making it one of the best calorie-to-protein ratios of any animal protein. It’s especially useful for cutting phases, high-protein snacks, or post-workout meals where you want high satiety without a lot of fat or carbs.

This is also why tuna is a staple in bodybuilding diets and transformation plans, it delivers serious results on minimal calories when combined with smart carbs and vegetables.

Tuna vs. Other Tinned Proteins

Canned tuna beats most other tinned proteins in calorie control. Compared to:

  • Canned salmon: higher in calories and fat (good fats, but more energy-dense)
  • Canned sardines: higher in fat and often come packed in oil
  • Tinned beans or lentils: more carbs, less protein per calorie
  • Tinned chicken: similar calorie count, but lower omega-3 content

Tuna stands out as one of the leanest, highest-protein options per gram available in the tinned food aisle.

Summary

A can of tuna contains between 100 and 220 calories, depending on whether it's packed in water, brine, or oil. Tuna in spring water or brine is the leanest choice, making it ideal for calorie-conscious diets. Rich in protein and nutrients, tuna offers excellent satiety and flexibility in meal planning but be mindful of oil-packed versions and mercury intake if you eat it often. For anyone focused on high-protein eating or weight loss, tuna remains one of the most efficient calorie-to-nutrient ratio foods available.

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