Enter weight and age to see the dose.
Dose per administration
0 mg
- Total per day
- –
- Daily dose per kg
- –
- Volume per dose
- –
- Basis
- –
Reference aid only. Confirm against the BNFc, NICE or your local antimicrobial guideline, and adjust for allergy and kidney function.
Cefalexin Dose Calculator
This calculator works out a cefalexin (cephalexin) dose for children by weight, or a fixed dose for those aged 12 and over. It shows the dose in milligrams, how often to give it, the total for the day, and the volume of suspension to measure for the strength you have.
How the dose is calculated
The calculator follows the UK approach in the BNFc and NICE antibiotic guidance for children:
| Age | Standard infection | Severe infection |
|---|---|---|
| 1 month to 11 years | 12.5 mg/kg twice daily (or about 8.3 mg/kg three times daily) | 25 mg/kg two to four times daily, up to 1 g per dose |
| 12 years and over | 500 mg two or three times daily | 1 g three or four times daily |
- For standard dosing the daily total is 25 mg/kg, split into two or three doses. A single dose is capped at 500 mg.
- The volume is dose ÷ concentration:
mL = mg ÷ (mg per mL). A 125 mg/5 mL suspension is 25 mg/mL; a 250 mg/5 mL suspension is 50 mg/mL. - For 12 years and over the BNFc allows 1 to 1.5 g per dose in severe infection. The calculator gives 1 g, the lower figure, and leaves higher doses to the prescriber.
Other guidelines
Recommendations differ between countries. Some Australian and Irish guidelines, for example, use 20 mg/kg three times daily or fixed age-band doses. Always follow the guidance used where you work, and treat this calculator as the arithmetic for the BNFc/NICE regimen.
Safety points
- Cefalexin is a first-generation cephalosporin. Avoid it in anyone with cephalosporin hypersensitivity.
- Cross-reactivity with penicillin allergy can occur; the risk is greater with severe or immediate reactions.
- Reduce the dose or lengthen the interval in significant kidney impairment.
- Diarrhoea is the commonest side effect. Persistent or severe diarrhoea should be reviewed, as it can rarely signal Clostridioides difficile infection.
- Give a full course as directed, and check that the indication and duration match local antimicrobial guidance.
Frequently asked questions
How much cefalexin is given to a child?
For standard infections, 25 mg/kg a day, divided into two or three doses (12.5 mg/kg twice daily). For severe infections, 25 mg/kg per dose up to four times daily, with a maximum of 1 g per dose.
What dose do teenagers take?
From 12 years, 500 mg two or three times daily, and 1 g three or four times daily for severe infection.
Is cefalexin safe with a penicillin allergy?
Often yes, but cross-reactivity can occur. It should be avoided if the penicillin reaction was severe or immediate unless a specialist advises otherwise.
How long is a course?
It depends on the infection. Many skin and soft-tissue courses run 7 to 10 days, but follow your local guideline for the specific indication.
Why do doses in different countries differ?
Guidelines use different regimens, such as 12.5 mg/kg twice daily in the UK and 20 mg/kg three times daily in some Australian hospitals. Use the one your local guideline specifies.
Medical disclaimer
This calculator is a reference aid for healthcare professionals. It follows one published regimen and does not replace the BNFc, NICE guidance, your local antimicrobial policy, the product information or clinical judgement. It does not account for allergy, renal function or the specific infection.
Sources & references
- NICE. British National Formulary for Children (BNFc) — cefalexin monograph. bnfc.nice.org.uk
- Health Service Executive (Ireland). Cefalexin — antibiotic prescribing for children. hse.ie
- Médecins Sans Frontières. Essential drugs: Cefalexin oral. medicalguidelines.msf.org