How this instrument works
Mercury builds up in fish and shellfish because it's present at low levels throughout ocean and freshwater ecosystems, and it concentrates as it moves up the food chain — larger, longer-lived predatory fish like marlin and swordfish accumulate far more than smaller, shorter-lived species like tilapia or shrimp. Karimi, Fitzgerald & Fisher's 2012 meta-analysis in Environmental Health Perspectives compiled mercury concentrations (in parts per million) across common commercial seafood species from government and academic data, giving a solid reference point for how much a species typically carries.
This calculator multiplies your chosen species' typical mercury concentration by your serving size to estimate the mercury in that one meal, then compares it against a weekly safe-intake reference based on the EPA's mercury reference dose of 0.1 microgram per kilogram of body weight per day — equivalently 0.7 micrograms per kilogram per week — scaled to your body weight.
The result, shown as a percentage of your weekly safe limit used by a single serving, is a way to see at a glance whether one meal of a given species is a small fraction of the weekly guidance or uses most or all of it in one sitting. This is a general-awareness estimate built from published population averages, not a personalized medical calculation — for guidance tailored to pregnancy, breastfeeding, or a child's diet, follow official FDA/EPA fish advisories or talk to a doctor.
- Choose Fish / seafood type — species with their published mean mercury concentration in ppm.
- Enter Serving size — the weight of the portion you're eating, in grams.
- Enter Body weight — used to scale the weekly safe-intake reference to you.
- Read Mercury in this serving and Share of weekly safe limit used by this serving.
Worked example — a swordfish serving for a 70 kg adult
Swordfish carries a mean mercury concentration of 0.893 ppm per Karimi, Fitzgerald & Fisher (2012). A 150 g serving contains 150 × 0.893 ≈ 133.95 micrograms of mercury. For a 70 kg adult, the weekly safe-intake reference is 70 × 0.7 = 49 micrograms, based on the EPA's 0.1 µg/kg/day reference dose.
That single 150 g swordfish serving uses 133.95 ÷ 49 × 100 ≈ 273% of that adult's weekly safe limit — well over the full week's guidance in one meal. This is exactly why regulatory fish advisories flag swordfish, along with marlin, shark, and wild bluefin tuna, as high-mercury species to limit, especially for anyone eating fish more than once a week.
Questions
Which fish have the highest and lowest mercury levels?
Per Karimi, Fitzgerald & Fisher's 2012 meta-analysis, marlin (1.517 ppm), swordfish (0.893 ppm), shark (0.882 ppm), and wild bluefin tuna (0.796 ppm) rank highest — all large, long-lived predatory species. Tilapia (0.019 ppm), clams (0.028 ppm), shrimp (0.053 ppm), and salmon (0.048 ppm) rank lowest, being smaller, shorter-lived, or lower on the food chain.
Where does the '0.7 µg/kg/week' safe-limit figure come from?
It's the EPA's mercury reference dose of 0.1 microgram per kilogram of body weight per day, expressed as a weekly total (0.1 × 7 = 0.7) rather than a daily one, since most people don't eat fish every single day — a weekly framing fits real eating patterns better. The FDA uses the same underlying reference dose in its joint fish consumption guidance with the EPA.
Is this calculator medical advice?
No — it's a general-awareness tool using published population-average mercury concentrations and a standard regulatory reference dose, not a personalized health assessment. Mercury sensitivity and guidance differ meaningfully for pregnant women, breastfeeding mothers, and young children, who are advised to follow the official EPA/FDA joint fish advisory specifically, and anyone with a specific health concern about mercury exposure should talk to a doctor rather than rely solely on this estimate.
Does going over 100% in one serving mean I've been poisoned?
No — the weekly reference dose is a conservative, precautionary guideline with built-in safety margins, designed so that staying under it over time keeps exposure well below levels associated with harm, not a hard toxicity threshold that triggers symptoms the moment it's crossed. One high-mercury meal that exceeds 100% of the weekly figure is a signal to go easy on high-mercury species for the rest of that week, not a medical emergency.
Why does body weight affect the safe limit?
Because the EPA's reference dose is defined per kilogram of body weight, reflecting that a given amount of mercury has a larger relative effect in a smaller body — the same logic used for many dose-based health and drug guidelines. That's why this calculator asks for body weight and scales the weekly safe-intake figure to it rather than using one fixed number for every adult.