Result in Micrograms
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Equivalent mass
Accurate mass conversion between milligrams (mg) and micrograms (µg / mcg) — and back
Convert milligrams to micrograms instantly using the exact factor of 1,000 µg per mg. Full multi-unit breakdown into µg, ng, g, kg, grains, and oz — all in one free tool for 2026.
Professional mass conversion for pharmaceuticals, nutrition, supplements, chemistry, toxicology, and laboratory science
The milligram and the microgram are both SI metric units of mass, connected by an exact factor of 1,000. By definition, 1 mg = 1,000 µg and 1 µg = 0.001 mg — perfectly exact, no rounding involved. This follows directly from the SI prefix hierarchy: milli- = 10⁻³ and micro- = 10⁻⁶, so 1 mg = 10⁻³ g and 1 µg = 10⁻⁶ g, giving a ratio of exactly 10³ = 1,000. The microgram is also commonly abbreviated as mcg in medical and pharmaceutical contexts — particularly on supplement and medication labels — to avoid misreading the Greek letter µ as "m", which could cause dangerous confusion between micrograms and milligrams in clinical settings.
Switch instantly between Milligrams → Micrograms and Micrograms → Milligrams conversion modes. The results panel simultaneously displays the equivalent mass in seven units — µg, mg, nanograms (ng), grams (g), kilograms (kg), grains (gr), and ounces (oz) — giving complete cross-unit context from a single input. This is especially valuable for pharmacists, dietitians, and laboratory scientists who routinely work across mg-scale drug doses, µg-scale nutrient RDAs (recommended dietary allowances), and ng-scale trace substance measurements — allowing immediate visibility of all relevant mass scales at once.
The mg-to-µg conversion is one of the most safety-critical in healthcare and science: Pharmaceuticals — drug dosages range from µg (e.g., fentanyl 25 µg patch, levothyroxine 50 µg tablet) to mg (e.g., paracetamol 500 mg tablet); Nutrition & vitamins — vitamin D (400–2000 IU = 10–50 µg), folate (400 µg), B12 (2.4 µg), iron (8–18 mg); Toxicology — lethal doses expressed in µg/kg (e.g., botulinum toxin LD50 ≈ 1.3–2.1 ng/kg); Laboratory analysis — HPLC, mass spectrometry, and immunoassay concentrations; Environmental testing — pesticide and heavy metal limits in µg/kg or µg/L (ppb).
Select conversion direction, enter your mass value, and get instant multi-unit results
The milligram (mg) is one-thousandth of a gram (10⁻³ g) — the standard unit for everyday medication doses, food nutrient content on labels, and small-scale chemical measurements. The microgram (µg), also written as mcg, is one-millionth of a gram (10⁻⁶ g) — exactly one-thousandth of a milligram. The microgram is the primary unit for trace nutrients, potent pharmaceutical compounds, hormone levels, and environmental contaminant thresholds. Together, these two units cover the mass range from everyday supplement doses down to the concentrations relevant in endocrinology, toxicology, and environmental chemistry.
The conversion is perfectly exact: 1 mg = 1,000 µg and 1 µg = 0.001 mg = 10⁻³ mg. In the broader SI mass hierarchy: 1 g = 1,000 mg = 1,000,000 µg = 1,000,000,000 ng. The microgram is critically important in medicine because many highly potent drugs — thyroid hormones, fentanyl, cyanocobalamin (B12), calcitriol (active vitamin D), and folate — are prescribed or recommended in microgram doses, while common OTC medications like paracetamol, ibuprofen, and aspirin are dosed in hundreds of milligrams. A 10× dosing error between mg and µg (or vice versa) can be immediately life-threatening — making clear, accurate conversion a genuine patient safety requirement.
Example: 0.4 mg × 1,000 = 400 µg (folate RDA) | 50 µg ÷ 1,000 = 0.05 mg (vitamin D dose)
1 mg = 1,000 µg | 1 µg = 1,000 ng | 1 mg = 10⁶ ng | 1 g = 10³ mg = 10⁶ µg = 10⁹ ng | 1 grain = 64.79891 mg
To convert milligrams to micrograms, multiply by 1,000 (move the decimal point three places to the right). To convert micrograms back to milligrams, divide by 1,000 (move the decimal three places to the left). Here are three practical worked examples:
Input: 0.4 mg (RDA for adults)
Formula: 0.4 × 1,000
= 400 µg
= standard folate supplement dose
Input: 25 µg (1,000 IU vitamin D3)
Formula: 25 ÷ 1,000
= 0.025 mg
= common daily vitamin D tablet
Input: 500 mg (standard tablet)
Formula: 500 × 1,000
= 500,000 µg
= 500 mg paracetamol in micrograms
mg → µg: Multiply by 1,000 — move decimal 3 places right. Example: 0.025 mg → 25 µg; 1.5 mg → 1,500 µg; 200 mg → 200,000 µg. µg → mg: Divide by 1,000 — move decimal 3 places left. Example: 400 µg → 0.4 mg; 2.4 µg → 0.0024 mg; 50 µg → 0.05 mg. Key nutrient doses: Folate RDA = 400 µg (0.4 mg); Vitamin B12 RDA = 2.4 µg (0.0024 mg); Vitamin D3 (1,000 IU) = 25 µg (0.025 mg); Iodine RDA = 150 µg (0.15 mg); Selenium RDA = 55 µg (0.055 mg); Vitamin K RDA ≈ 90–120 µg (0.09–0.12 mg). Pharmaceutical doses: Levothyroxine = 25–200 µg (0.025–0.2 mg); Fentanyl patch = 12–100 µg/hr; Cyanocobalamin injection = 1,000 µg (1 mg). mcg = µg: Both abbreviations mean exactly the same unit — micrograms. mcg is preferred on medical labels to avoid misreading µ.
Complete reference table from trace nutrient doses through pharmaceutical and food-science quantities, with µg, ng, g, grain, and real-world pharmaceutical/nutritional context. Desktop shows the full table; mobile shows grouped cards.
| Milligrams (mg) | Micrograms (µg/mcg) | Nanograms (ng) | Grams (g) | Grains (gr) | Real-World Reference |
|---|---|---|---|---|---|
| 0.001 mg | 1 µg | 1,000 ng | 0.000001 | 0.0000154 | Trace amount / vitamin B12 fraction |
| 0.0024 mg | 2.4 µg | 2,400 ng | 0.0000024 | 0.0000370 | Vitamin B12 daily RDA (adults) |
| 0.005 mg | 5 µg | 5,000 ng | 0.000005 | 0.0000772 | High-dose B12 / trace mineral |
| 0.010 mg | 10 µg | 10,000 ng | 0.000010 | 0.000154 | Low-dose thyroid medication |
| 0.025 mg | 25 µg | 25,000 ng | 0.000025 | 0.000386 | Vitamin D3 — 1,000 IU tablet |
| 0.050 mg | 50 µg | 50,000 ng | 0.000050 | 0.000772 | Levothyroxine 50 µg tablet / Vit D 2,000 IU |
| 0.100 mg | 100 µg | 100,000 ng | 0.000100 | 0.00154 | Folic acid supplement / iodine dose |
| 0.150 mg | 150 µg | 150,000 ng | 0.000150 | 0.00231 | Iodine RDA (adults) |
| 0.200 mg | 200 µg | 200,000 ng | 0.000200 | 0.00309 | Levothyroxine max dose / selenium range |
| 0.400 mg | 400 µg | 400,000 ng | 0.000400 | 0.00617 | Folate / folic acid RDA for adults |
| 0.800 mg | 800 µg | 800,000 ng | 0.000800 | 0.01235 | Folate dose in pregnancy |
| 1.000 mg | 1,000 µg | 1,000,000 ng | 0.001000 | 0.01543 | 1 mg — cyanocobalamin injection |
| 5.000 mg | 5,000 µg | 5,000,000 ng | 0.005000 | 0.07716 | High-dose folic acid (therapeutic) |
| 10.000 mg | 10,000 µg | 10,000,000 ng | 0.010000 | 0.15432 | Iron supplement (low dose) |
| 50.000 mg | 50,000 µg | 50,000,000 ng | 0.050000 | 0.77162 | Vitamin C (low dose) / zinc supplement |
| 100.000 mg | 100,000 µg | 100,000,000 ng | 0.100000 | 1.54324 | Aspirin (low-dose) / magnesium tablet |
| 200.000 mg | 200,000 µg | 200,000,000 ng | 0.200000 | 3.08647 | Ibuprofen (low dose) / vitamin C tablet |
| 500.000 mg | 500,000 µg | 500,000,000 ng | 0.500000 | 7.71618 | Paracetamol / Amoxicillin standard tablet |
| 1,000 mg | 1,000,000 µg | 1,000,000,000 ng | 1.000000 | 15.4324 | 1 gram — high-dose antibiotic / Vit C |
| 5,000 mg | 5,000,000 µg | 5,000,000,000 ng | 5.000000 | 77.162 | 5 g — IV dose / bulk supplement |
🟢 Green = trace / µg-scale nutrients | 🟧 Orange = mg-scale pharmaceutical doses | 🔵 Blue = gram-scale doses
Drug doses span a wide mass range requiring accurate mg-to-µg conversion. Thyroid hormones (levothyroxine) are prescribed in microgram doses: 25 µg, 50 µg, 75 µg, 100 µg, 125 µg, 150 µg, 175 µg, 200 µg — all less than 0.2 mg. Fentanyl patches deliver 12–100 µg/hour (0.012–0.1 mg/hr). Digoxin: 62.5–250 µg (0.0625–0.25 mg). Common OTC doses are in milligrams: paracetamol 500 mg = 500,000 µg; ibuprofen 200–400 mg; aspirin 300–500 mg (or 75–100 mg low-dose). Pharmacists dispensing compound medications or verifying prescriptions must convert between mg and µg dosing ranges accurately — a 1,000× error (e.g., giving 1 mg of levothyroxine instead of 1 µg) could be life-threatening.
Nutrition labels and dietary reference intakes (DRIs) use both mg and µg depending on the nutrient. Key nutrients in micrograms: Vitamin B12 RDA = 2.4 µg/day; Vitamin D RDA = 15–20 µg/day (600–800 IU); Folate RDA = 400 µg/day (800 µg in pregnancy); Iodine RDA = 150 µg/day; Selenium RDA = 55 µg/day; Vitamin K RDA = 90–120 µg/day; Chromium AI = 25–35 µg/day; Molybdenum RDA = 45 µg/day. Nutrients in milligrams: Vitamin C RDA = 75–90 mg/day; Iron RDA = 8–18 mg/day; Zinc RDA = 8–11 mg/day; Magnesium RDA = 310–420 mg/day. Dietitians and supplement formulators regularly convert between µg and mg when reviewing label compliance or calculating combined nutrient doses across multiple supplements.
Laboratory concentrations are frequently expressed at both the mg and µg scale. Common analytical expressions: mg/L = parts per million (ppm) in water; µg/L = parts per billion (ppb) in water; µg/mL = mg/L (same numeric value in aqueous solutions, density ≈ 1 g/mL). HPLC (high-performance liquid chromatography) standard solutions: typically 0.1–100 µg/mL. Mass spectrometry detection limits: often in the ng/mL to pg/mL range. Blood drug concentration (therapeutic monitoring): lithium ≈ 0.6–1.2 mmol/L; digoxin ≈ 0.5–2 µg/L; vancomycin 10–20 mg/L. Enzyme activity units: often in µg or nmol per minute per mg protein. Converting between mg-based reagent preparation and µg-scale assay concentrations is a daily laboratory task.
Toxicology relies heavily on µg-scale measurements. Lethal dose 50 (LD50) values for highly potent substances: Botulinum toxin LD50 ≈ 1–2 ng/kg (0.000001–0.000002 µg/kg); Ricin LD50 ≈ 22 µg/kg; VX nerve agent LD50 ≈ 10 µg/kg; fentanyl LD50 ≈ 3.1 mg/kg. Environmental regulatory limits: WHO drinking water guideline for arsenic = 10 µg/L (0.01 mg/L); lead in drinking water EU limit = 10 µg/L; mercury limit = 1 µg/L. Air quality: PM2.5 standard (WHO) = 5 µg/m³ annual mean; NO2 = 10 µg/m³. Food safety — maximum residue levels (MRLs) for pesticides are expressed in µg/kg or mg/kg. Forensic toxicologists, environmental chemists, and food safety analysts work continuously across mg/kg and µg/kg (ppm and ppb) scales.
Clinical laboratory blood and urine tests report many biomarkers in µg and mg units. Serum ferritin: normal range 12–300 µg/L. Vitamin B12 serum level: 200–900 pg/mL (= 0.2–0.9 µg/L). Folate (serum): 3–17 µg/L. Thyroid-stimulating hormone (TSH): 0.4–4.0 mIU/L. Creatinine (urine): 800–2,000 mg/day. Urinary albumin: normal <30 mg/g creatinine; microalbuminuria 30–300 mg/g; macroalbuminuria >300 mg/g. 24-hour urine protein: normal <150 mg/day. Haemoglobin A1c: reported as %; average blood glucose in mg/dL or mmol/L. Drug monitoring in plasma: many therapeutic drug levels in µg/mL. Clinicians, nurses, and pharmacists interpreting laboratory reports must readily convert between these mass scales to assess patient status and adjust dosing.
The supplement and nutraceutical industry uses both mg and µg on product labels, requiring frequent conversion for compliance with regulatory label requirements. Vitamins in µg: B12, D, K, folate, biotin (30 µg RDA = 0.03 mg), chromium, iodine, molybdenum, selenium. Vitamins in mg: A (retinol activity equivalents: 700–900 µg RAE = 0.7–0.9 mg), C, E (15 mg = 22.4 IU), B1, B2, B3, B5, B6. US FDA requires supplement facts panels to list nutrients in the units specified in 21 CFR 101.9; the EU NRV system (Nutrient Reference Values) specifies some vitamins in µg and others in mg. International supplement manufacturers exporting between the US, EU, UK, and Australia must convert between different labelling standards that may use µg and mg differently for the same nutrient.
1 mg = 1,000 µg (exact). 1 µg = 0.001 mg. 1 mg = 1,000,000 ng. 1 µg = 1,000 ng. 1 g = 1,000 mg = 1,000,000 µg. 1 grain = 64.79891 mg = 64,798.91 µg. Key nutrient RDAs: Folate 400 µg (0.4 mg); Vitamin D 15 µg (0.015 mg / 600 IU); Iodine 150 µg (0.15 mg); B12 2.4 µg (0.0024 mg); Selenium 55 µg (0.055 mg). Common drug doses in µg: Levothyroxine 25–200 µg; Fentanyl patch 25–100 µg/hr; Ethinylestradiol (pill) 20–35 µg. mcg = µg: Identical unit, different abbreviation — both mean micrograms. Quick rule: mg × 1,000 = µg; µg ÷ 1,000 = mg. Exact powers of 10 — no approximation required.
Confusing milligrams (mg) with micrograms (µg or mcg) is a well-documented cause of serious medication errors in healthcare settings. Since 1 mg = 1,000 µg, a patient receiving a dose in mg when it should be µg receives 1,000 times the intended dose — potentially fatal for potent drugs like fentanyl, levothyroxine, or warfarin. The Institute for Safe Medication Practices (ISMP) specifically recommends: never abbreviate microgram as µg on handwritten prescriptions — always write "mcg" or "micrograms" in full to prevent misreading µ as m (milligrams). In pharmacy, "1 mg" of levothyroxine is 1,000× the maximum typical dose (0.2 mg). Always double-check the unit on drug labels — confirm whether a dose is in mg or mcg/µg before dispensing, administering, or consuming any medication or supplement.
The International Bureau of Weights and Measures (BIPM) defines the kilogram as the SI base unit of mass, with milligrams (10⁻⁶ kg) and micrograms (10⁻⁹ kg) as derived units using the milli- and micro- SI prefixes. The 9th edition SI Brochure (2019) confirms all SI prefix multipliers and the exact relationships between mass units. The gram, milligram, and microgram are all coherent derived units within the SI, fully defined by the Planck constant-based kilogram definition adopted in 2019.
Visit BIPM →The Institute for Safe Medication Practices (ISMP) maintains a list of error-prone abbreviations including µg vs mg, and specifically recommends writing "mcg" rather than "µg" on handwritten prescriptions and medication administration records to prevent dangerous 1,000× dosing errors. ISMP publications document numerous real-world cases of microgram-milligram confusion in clinical settings and provide evidence-based guidance for safe drug labelling, prescription writing, and medication administration procedures in healthcare facilities worldwide.
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