Medication Conversion Calculator
Medication doses are written in whichever metric mass unit fits the drug: micrograms for potent medicines dosed in tiny amounts, milligrams for most tablets, grams for bulk powders and kilograms almost never outside manufacturing. This calculator converts one dose between those four units, micrograms (mcg), milligrams (mg), grams (g) and kilograms (kg), using the exact powers of 1,000 that link them. It converts mass only, on purpose: turning a dose into millilitres needs the product’s concentration, and International Units measure potency rather than mass, so both of those jobs belong to different tools, linked further down.
This tool converts the mass of a dose only. It does not check whether a dose is safe or appropriate for any patient, drug or condition. Always verify a converted dose against the original order and your local protocol before administering.
Quick Answer
The pre-filled example converts 500 milligrams to 500,000 micrograms: every step between neighbouring mass units is a factor of 1,000, so mg to mcg multiplies by 1,000, mg to g divides by 1,000, and g to kg divides by 1,000 again. The calculator prints the result to six decimal places (500000.000000) so that very small conversions, such as 1 mcg = 0.000001 g, stay visible instead of rounding away to zero.
Key takeaways
- The metric mass ladder used in prescribing has four rungs: kg, g, mg, mcg. Each rung is exactly 1,000 times the one below it, with no rounding anywhere in the system.
- Mixing up mg and mcg is a 1,000-fold dosing error, the single most dangerous slip in this corner of clinical arithmetic.
- This tool converts mass only. Millilitres need a concentration, International Units measure potency rather than mass, and mg/kg dosing needs the patient's weight: three different jobs, each handled elsewhere on this site.
- Write "mcg" rather than the micro symbol, keep a leading zero on decimal doses, and drop trailing zeros: the notation rules in the safety section below come from the Institute for Safe Medication Practices.
- Quick Answer
- How to use the medication conversion calculator
- The formula: one ladder, three steps of 1,000
- Worked example: 500 mg in micrograms, checked in reverse
- Strengths you will actually meet on labels
- Writing the converted dose so nobody misreads it
- What this converter deliberately leaves out
- What competing calculators miss
- Frequently asked questions
- Add This Calculator to Your Website
How to use the medication conversion calculator
Enter the dose, pick the unit it is written in, pick the unit you need, and click Calculate. The result appears as a full sentence, dose and both units spelled out, so it can be read back against the order word for word.
- Read the dose off the order or label exactly: number and unit together. 0.25 mg and 250 mcg are the same dose written two ways; 0.25 mcg is a thousand times smaller. The unit is part of the dose.
- Type the number and set From unit: the worked example starts at 500 mg. If the label uses the micro symbol (µg) or "ug", that is micrograms: choose Micrograms (mcg).
- Set the To unit and calculate: the badge under the result states the exact factor the tool applied, for example "1 mg = 1,000 mcg", so a second person checking your work can see the reasoning, not just the answer.
- Independently verify before use: run the conversion backwards (convert the result back to the original unit) and confirm you land on the starting figure. A round-trip check catches a wrong From or To selection, which is the mistake this kind of tool cannot detect for you.
The formula: one ladder, three steps of 1,000
Converted dose = Dose × (micrograms per From unit) ÷ (micrograms per To unit). The calculator routes every conversion through micrograms, the smallest of the four units, using the exact SI mass relationships maintained in the BIPM SI Brochure: 1 kg = 1,000 g, 1 g = 1,000 mg, 1 mg = 1,000 mcg.
1 kg = 1,000,000,000 mcg | 1 g = 1,000,000 mcg | 1 mg = 1,000 mcg | 1 mcg = 1 mcg
| From \ To | mcg | mg | g | kg |
|---|---|---|---|---|
| 1 mcg | 1 | 0.001 | 0.000001 | 0.000000001 |
| 1 mg | 1,000 | 1 | 0.001 | 0.000001 |
| 1 g | 1,000,000 | 1,000 | 1 | 0.001 |
| 1 kg | 1,000,000,000 | 1,000,000 | 1,000 | 1 |
Because every factor is a power of ten, a conversion never introduces rounding error of its own: any inaccuracy in the result came from the number typed in, not from the arithmetic. That is also why the tool can safely print six decimal places. The decimals are not false precision; they are what keep a microgram-to-gram conversion (0.000001 g per mcg) from displaying as zero.
Worked example: 500 mg in micrograms, checked in reverse
A stock bottle is labelled in milligrams and the order is written in micrograms: convert 500 mg to mcg. The calculator is pre-filled with exactly this job.
Reverse check: convert 500,000 mcg back to milligrams and the tool returns 500.000000 milligrams (mg), the starting figure. Two more real runs worth knowing by sight: 0.25 mg converts to 250.000000 micrograms (mcg), the classic digoxin-strength pairing, and 3.75 g converts to 3750000.000000 micrograms (mcg). If a result ever surprises you by a factor of about 1,000, the From or To unit is almost certainly set wrong; that pattern is the fingerprint of a rung skipped on the ladder.
Strengths you will actually meet on labels
Manufacturers pick the unit that keeps the printed number between 1 and 1,000, so the same strength appears in mg on one product and mcg on another. These are the pairings that come up constantly in practice, each one a real run of the calculator above:
| Milligrams (mg) | Micrograms (mcg) | Where you meet it |
|---|---|---|
| 0.05 mg | 50 mcg | Low levothyroxine strengths |
| 0.125 mg | 125 mcg | Digoxin 125 microgram tablets, also written 0.125 mg |
| 0.25 mg | 250 mcg | Digoxin top strength; common inhaler puff strengths |
| 0.5 mg | 500 mcg | Vitamin B12 doses, often labelled 500 mcg or 1,000 mcg |
| 1 mg | 1,000 mcg | Folic acid 1 mg; B12 1,000 mcg ampoules |
| 5 mg | 5,000 mcg | Folic acid 5 mg tablets |
The digoxin row is the one to respect. Digoxin has a narrow gap between a therapeutic dose and a toxic one, it is prescribed in micrograms, and its strengths (62.5, 125 and 250 mcg) sit one misread decimal away from milligram figures. The AHRQ patient-safety literature treats dose-unit errors of exactly this kind as a recurring, preventable source of harm, which is why the AHRQ PSNet primer on medication errors and adverse drug events keeps being cited in training: the errors are ordinary, and the defences are ordinary too, such as reading the unit aloud and converting with a tool rather than in your head.
Writing the converted dose so nobody misreads it
A correct conversion can still be written down dangerously. The notation rules below come from the Institute for Safe Medication Practices list of error-prone abbreviations, symbols and dose designations, the standard reference US hospitals work to:
- Write mcg, never the micro symbol. A handwritten µg is easily read as mg, which silently multiplies the dose by 1,000.
- Always use a leading zero: 0.5 mg, never.5 mg. A faint decimal point turns.5 into 5, a tenfold overdose.
- Never use a trailing zero on a whole number: 1 mg, never 1.0 mg. A missed decimal point turns 1.0 into 10.
- Use commas or words for large numbers: 100,000 units or "100 thousand", so digit-counting errors show up.
- Spell the unit out when there is any doubt: "micrograms" in full cannot be misread as anything else.
The six-decimal output of this calculator is machine formatting, meant for checking, not for transcription onto a chart. When you write the dose down, round and format it the way the rules above require: 500,000 mcg, not 500000.000000 mcg.
What this converter deliberately leaves out
Three neighbouring jobs look like unit conversion but are not, and folding them into this tool with invented factors would be unsafe. Each has a dedicated calculator on this site:
- Mass to volume (mg to mL): needs the concentration printed on the specific product, because 500 mg is 10 mL of a 250 mg/5 mL suspension and 2 mL of a 250 mg/mL injection. The milligrams to millilitres calculator asks for that concentration.
- International Units (IU): an IU measures biological effect, and its mass equivalent is fixed substance by substance. There is no universal IU factor to build into a converter honestly.
- Weight-based dosing (mg/kg): needs the patient's weight and a judgement about the safe range for that drug. The med dosage calculator handles the per-kilogram working, and drug-specific tools such as the amoxicillin pediatric dosing calculator handle the ranges for individual medicines.
What competing calculators miss
Dose-unit tools tend to fail in one of three directions:
- Single-pair converters (mgtomcg.com, Calxify's mg-to-mcg page): fine for the one pair in their title, but a nurse converting grams to micrograms or kilograms to milligrams has to find another page, and the pair-specific pages rarely show the factor they applied.
- Everything-in-one dose tools (SageCalculator's dose conversion page, Medplore's concentration calculator): they bundle mass conversion with concentration, weight-based dosing and even animal scaling on one screen. Breadth sounds helpful until a user enters a mass into a volume field; the failure mode is silent, and in dosing a silent failure is the dangerous kind.
- Reference-table pages (NursingCalc's drug unit converter): the strongest rival format, with common-strength tables worth copying in spirit. Its converter, though, gives no factor readout and no six-decimal guard for tiny results, so a mcg-to-kg conversion displays as a row of zeros.
- The gap this page fills: all twelve ordered pairs among the four mass units in one tool, the applied factor printed under every result, six decimals so small conversions stay visible, a common-strengths table, the ISMP writing rules on the same page, and an explicit statement of what the tool refuses to convert, with the right tool linked for each refusal.
Frequently asked questions
Multiply the milligram figure by 1,000. One milligram is exactly 1,000 micrograms, so 2.5 mg becomes 2,500 mcg. To go the other way, divide the microgram figure by 1,000: 250 mcg becomes 0.25 mg. The calculator does the same arithmetic for grams and kilograms, which sit one and two rungs further up the ladder.
Exactly 1,000. A microgram is one millionth of a gram and a milligram is one thousandth of a gram, so the two units are three powers of ten apart. That is why confusing them is so dangerous: reading mg as mcg, or mcg as mg, changes a dose by a factor of 1,000.
Yes. 500 micrograms is half of 1,000 micrograms, and 1,000 micrograms is 1 milligram, so 500 mcg and 0.5 mg are the same mass written two ways. Labels use whichever unit keeps the number readable, which is why levothyroxine strengths are printed in micrograms (25 mcg to 300 mcg) while many tablets are printed in milligrams.
Because some conversions produce very small numbers that would disappear at fewer decimals. One microgram is 0.000001 grams, a figure that rounds to 0.00 at two decimals but stays visible at six. For everyday conversions you can ignore the trailing zeros: 500000.000000 mcg is simply 500,000 mcg.
No. Milligrams measure mass and millilitres measure volume, and the bridge between them is the concentration of the specific product, such as 250 mg per 5 mL. The same 500 mg dose is 10 mL of one suspension and 2 mL of a stronger injection, so a mass-to-volume conversion without the concentration would be a guess. Use a concentration-based tool with the figure from your product label instead.
No, and no honest converter can do it with a single factor. An International Unit measures biological potency, not mass, and the mass behind 1 IU is set separately for each substance: 1 IU of vitamin D is 0.025 mcg, while 1 IU of insulin or of vitamin E corresponds to a completely different mass. Convert IU only with the factor published for that specific drug or vitamin.
Because a handwritten or poorly printed micro symbol can be misread as the letter m, turning mcg into mg and multiplying the dose by 1,000. The Institute for Safe Medication Practices keeps the symbol on its error-prone abbreviations list and recommends writing mcg instead. The same list advises a leading zero before decimal doses (0.5 mg, never.5 mg) and no trailing zero after a whole-number dose (1 mg, never 1.0 mg).
No. It converts a finished dose between mass units; it does not multiply a per-kilogram rate by a patient's weight, and it does not judge whether a dose sits inside a safe range for any drug. Weight-based working and safe-range checks need a dosage calculator and the drug's own reference ranges, and every converted dose still needs an independent check against the original order.
Add This Calculator to Your Website
Embed this calculator on your own site with the code below. Pick a size to preview it live, then copy the code.
Powered by Calculator Zilo
References
- Bureau International des Poids et Mesures (BIPM). The International System of Units (SI Brochure). Accessed October 22, 2026.
- Centers for Disease Control and Prevention, Emerging Infectious Diseases. Units of Measure (SI unit symbols, including mg and mcg). Accessed October 22, 2026.
- Taber's Medical Dictionary. Units of Measurement (Including SI Units): prefixes, multiples and metric masses. Accessed October 22, 2026.
- Institute for Safe Medication Practices (ISMP). ISMP's List of Error-Prone Abbreviations, Symbols, and Dose Designations. Accessed October 22, 2026.
- National Library of Medicine, MedlinePlus. Medication Errors. Accessed October 22, 2026.
- National Library of Medicine, MedlinePlus Medical Encyclopedia. Liquid Medication Administration (unit conversions for mL, teaspoons and tablespoons). Accessed October 22, 2026.
- National Library of Medicine, MedlinePlus Medical Encyclopedia. Medicine Safety: Filling Your Prescription. Accessed October 22, 2026.
- National Library of Medicine, MedlinePlus Medical Encyclopedia. Help Prevent Hospital Errors. Accessed October 22, 2026.
- Agency for Healthcare Research and Quality, PSNet. Medication Errors and Adverse Drug Events (PSNet Primer). Accessed October 22, 2026.
- Agency for Healthcare Research and Quality, PSNet. Medication Errors in Retail Pharmacies: Wrong Patient, Wrong Instructions (WebM&M case). Accessed October 22, 2026.