Find out how much mercury you're getting from fish - personalised to your weight, diet, and life stage.
Fish is among the healthiest foods on the planet - rich in omega-3 fatty acids, high-quality protein, vitamin D, and iodine. Yet virtually all fish contain trace amounts of mercury, a naturally occurring heavy metal that becomes concentrated in the ocean food chain. For most healthy adults, the mercury in fish poses no meaningful risk when consumption is moderate and species choices are sensible. But for pregnant women, nursing mothers, and young children, the stakes are higher: methylmercury - the organic form found in fish tissue - is a potent neurotoxin that can affect the developing brain and nervous system.
This calculator uses real FDA monitoring data on mercury concentrations (measured in parts per million, or ppm) to give you a personalised estimate of your weekly mercury intake versus the EPA's Reference Dose (RfD) - the scientifically established safe limit.
Mercury enters the environment from both natural sources (volcanic activity, erosion of mineral deposits) and human activities (coal-fired power plants, mining, industrial processes). Once released into the air, it settles into water bodies where bacteria convert it into methylmercury - the bioavailable form that living organisms absorb. Aquatic plants and microorganisms take up methylmercury, zooplankton eat the microorganisms, small fish eat the zooplankton, and larger predatory fish eat the smaller fish.
This process - called bioaccumulation and biomagnification - means that each step up the food chain concentrates mercury further. A large predatory fish like a swordfish or bluefin tuna can carry mercury concentrations 1 million times higher than the surrounding water. Bottom-feeders and filter feeders at the base of the food chain (sardines, oysters, clams) accumulate very little. This is why species choice matters so much.
Mercury in fish tissue is measured in milligrams per kilogram (mg/kg), which is equivalent to parts per million (ppm). The FDA has tested thousands of commercial fish samples over decades. Mean values range from around 0.003 ppm in farmed salmon to over 1.0 ppm in shark, swordfish, king mackerel, and bigeye tuna. This calculator uses these mean values - individual fish will vary, and cooking method does not meaningfully reduce mercury content.
The US Environmental Protection Agency (EPA) has established a Reference Dose (RfD) for methylmercury of 0.1 micrograms (µg) per kilogram of body weight per day. This limit is deliberately conservative - it includes a 10-fold safety factor over the dose at which no effects were observed in the most sensitive study populations. For a 70 kg adult, the weekly limit works out to 49 µg (0.1 × 70 × 7 days).
For a pregnant woman of the same weight, the same mathematical limit applies - but the clinical implications are more serious. The developing foetal brain is far more sensitive to methylmercury than the adult brain, and exposure during gestation has been linked to subtle deficits in cognitive development, language, attention, and fine motor skills, even when the mother shows no symptoms.
The FDA and EPA jointly advise:
These species consistently show very low mercury levels (<0.1 ppm) and are safe for all groups to eat frequently:
These species should be avoided by pregnant women and children, and eaten rarely by everyone else:
The key insight from nutritional epidemiology is that the benefits of fish consumption (omega-3s, protein, micronutrients) outweigh the risks from mercury for the vast majority of people, provided they make smart species choices. Here's how:
The mercury concentration of any individual fish depends on its age, size, location, and diet. FDA data reports mean values across many samples. This calculator gives you an estimate based on the best available population-level data - it's a risk-assessment tool, not a precise measurement of any specific meal.
If you're consistently near or above 80% of the limit, consider substituting one or more servings with lower-mercury alternatives. If you're well under the limit even on a high-fish diet, you're in a healthy range - continue enjoying fish for its substantial benefits.
The scientific consensus is clear: for most people, eating more fish is a net positive. Omega-3 fatty acids (EPA and DHA) found predominantly in oily fish reduce triglycerides, lower blood pressure, decrease inflammation, and support brain health across the lifespan. A 2021 meta-analysis in the British Medical Journal found that eating fish 2–4 times per week was associated with a 17% lower risk of cardiovascular mortality. Use this calculator to identify the right species and frequency for your body weight and life stage - then enjoy fish as a central part of a healthy, varied diet.