About the Fish Mercury Calculator
Fish absorb methylmercury from water and their food, and the amount builds up ("bioaccumulates") more in large, long-lived predatory species than in small, short-lived ones. This calculator estimates how much mercury you take in from eating fish and compares that figure to the U.S. Environmental Protection Agency's reference dose (RfD) for methylmercury, which is the daily exposure level considered safe over a lifetime.
The formula
Daily mercury intake, normalized to body weight, is calculated as:
Intake (µg/kg body weight/day) = [Mercury concentration (mg/kg) × Portion size (kg) × Meals per week] ÷ 7 ÷ Body weight (kg) × 1000
Mercury concentration is measured in parts per million (ppm), which is numerically identical to milligrams per kilogram (mg/kg). Multiplying concentration by portion size gives the mass of mercury eaten per meal; multiplying by meals per week and dividing by 7 gives an average daily dose; dividing by body weight and converting milligrams to micrograms (×1000) gives the standard exposure unit used by EPA: micrograms of mercury per kilogram of body weight per day (µg/kg/day).
The EPA reference dose
The EPA reference dose (RfD) for methylmercury is 0.1 microgram per kilogram of body weight per day (0.1 µg/kg/day). It was set using a benchmark-dose approach from studies of prenatal mercury exposure and includes a built-in safety margin, so it is intended to protect even the most sensitive groups — including a developing fetus — from measurable neurological risk over a lifetime of exposure at that level.
Typical mercury levels in common fish (FDA/EPA data)
- Shark: ~0.995 ppm (mg/kg) — among the highest of commonly eaten species.
- Swordfish: ~0.689 ppm — high; FDA/EPA advise limiting or avoiding for pregnant women and young children.
- Fresh or frozen tuna (bigeye/yellowfin): ~0.359 ppm.
- Canned light tuna: ~0.128 ppm — notably lower than fresh tuna because it uses smaller species like skipjack.
- Cod: ~0.086 ppm.
- Tilapia: ~0.041 ppm.
- Salmon: ~0.031 ppm — one of the lowest-mercury popular fish.
- Shrimp: ~0.013 ppm — among the lowest of all seafood.
These are average values compiled from FDA and EPA seafood monitoring data; actual mercury content varies by catch location, fish size, and age, so treat them as planning estimates rather than a lab measurement of a specific fish.
Why body weight and meal frequency both matter
A given amount of mercury produces a higher exposure dose (µg/kg/day) in a smaller body, which is why children and smaller adults reach a larger fraction of the reference dose from the same portion size than a larger adult would. Frequency compounds the effect: eating a high-mercury fish occasionally contributes far less average daily dose than eating it multiple times a week, because the calculator (like EPA guidance) works from an averaged weekly intake, not a single meal in isolation.
FDA/EPA consumption advice for sensitive groups
For women who are pregnant or breastfeeding, and for young children, FDA and EPA jointly recommend eating 2–3 servings (roughly 224–340 g total) per week of fish that are low in mercury, avoiding the highest-mercury species (shark, swordfish, king mackerel, tilefish from the Gulf of Mexico, marlin, orange roughy, and bigeye tuna) entirely, and limiting white (albacore) tuna to one serving per week.