Metronidazole Dose Calculator
Estimate weight-based metronidazole dosing in mg per dose and per day. Enter body weight, mg/kg and frequency to see the calculation, with an optional single-dose cap.
Updated 2026-06-14 · Free · No sign-up · Runs privately in your browser
Show the formula & steps
Educational estimate only. Always confirm dosing with a clinician, the product label, and a current formulary. Not medical advice.
How the Metronidazole Dose Calculator Works
Metronidazole is most often prescribed using weight-based dosing, expressed in milligrams per kilogram. This tool does that arithmetic for you. Enter the patient’s body weight in kilograms, the mg/kg for the regimen, and how many doses per day, and it returns the dose per administration and the total daily dose, with an optional single-dose cap so large patients do not exceed a typical adult dose.
This is an educational aid for checking the math, not a substitute for clinical judgment.
The Formula
Two simple multiplications drive the result:
Dose per administration = body weight (kg) × dose per kg (mg/kg) Total daily dose = dose per administration × doses per day
If the calculated per-dose amount is larger than the cap you enter, it is limited to the cap.
Worked Example
Take a child weighing 20 kg on a regimen of 7.5 mg/kg every 8 hours (three doses a day), with a 500 mg single-dose cap:
- Per dose = 20 × 7.5 = 150 mg (below the 500 mg cap, so no limiting applies)
- Doses per day = 3
- Total daily dose = 150 × 3 = 450 mg/day
For an 80 kg adult at the same 7.5 mg/kg, the raw per-dose figure would be 600 mg, but the 500 mg cap limits each dose to 500 mg.
Common Reference Points
| Scenario | Typical figure |
|---|---|
| Anaerobic infection, per dose | ~7.5 mg/kg every 6 to 8 hours |
| Common adult oral dose | 500 mg three times daily |
| Pediatric total daily dose | ~30 mg/kg/day, divided |
| General maximum | about 4 g per day |
Important Safety Note
Dosing depends on the specific infection, the patient’s age and weight, kidney and liver function, drug interactions, and local guidelines. Metronidazole also requires patients to avoid alcohol during and shortly after treatment. Use this calculator only to check arithmetic, and always confirm the final dose with a qualified clinician and the current prescribing information. This page is not medical advice.
Frequently asked questions
How is metronidazole dosed by weight?+
Metronidazole is commonly dosed in milligrams per kilogram of body weight. A frequent reference is about 7.5 mg/kg every 6 to 8 hours for anaerobic infections. Multiply body weight in kilograms by the mg/kg figure to get a single dose, then multiply by the number of doses per day.
What is the usual adult dose of metronidazole?+
A common adult oral dose is 500 mg three times a day for anaerobic or many protozoal infections, though regimens vary by indication. The maximum is generally 4 grams per day. Always follow the prescriber's instructions and the product label.
What is the pediatric dose of metronidazole?+
Pediatric regimens are often expressed as about 30 mg/kg/day divided into three or four doses, with the exact figure depending on the infection. This calculator lets you enter the mg/kg and doses per day so you can model a specific regimen.
Why is there a single-dose cap?+
Weight-based dosing in larger patients can exceed typical adult per-dose amounts, so many regimens cap a single dose, for example at 500 mg. The calculator applies an optional cap so the per-dose result never exceeds the value you enter.
Is this metronidazole calculator medical advice?+
No. It is an educational estimate of the arithmetic only. Actual dosing depends on the indication, age, renal and liver function, and other factors. Always confirm with a clinician, the prescribing information, and a current formulary before giving any medication.