Benadryl Dosage Calculator
Estimate a weight-based dose of Benadryl (diphenhydramine) using the common guideline of about 1 mg per kg of body weight per dose, capped at the usual adult maximum. Enter the body weight and the liquid concentration to see the dose in milligrams and in millilitres. This is an educational estimate only — always confirm dosing with a pharmacist or doctor and the product label.
Rates and fees change frequently. Always confirm the current figures
with the official authority before relying on this result.
Formula
Dose (mg) = body weight (kg) × dose per kg (mg/kg), capped at 50 mg per dose
- A common diphenhydramine guideline is roughly 1 mg per kg of body weight per dose.
- Liquid volume (mL) = dose (mg) ÷ concentration (mg/mL); product strengths vary (e.g. 2.5 mg/mL or 5 mg/mL), so always check the label.
- A single dose is usually capped near the adult maximum of 50 mg, and total daily dose is also limited — do not exceed label or professional guidance.
- Doses are typically repeated every 4 to 6 hours as needed.
- This is an educational estimate. Diphenhydramine is not recommended for young children without medical advice — confirm dosing with a pharmacist or doctor.
20 kg child at 1 mg/kg, 2.5 mg/mL liquid
Inputs
- Body Weight (kg): 20
- Dose per kg (mg/kg): 1
- Liquid Concentration (mg/mL): 2.5
Dose = 20 × 1 = 20 mg. With a 2.5 mg/mL liquid that's 20 ÷ 2.5 = 8 mL per dose, given every 4–6 hours as needed. Always confirm with a professional.
Frequently asked questions
How is the Benadryl dose calculated?
It multiplies body weight in kilograms by a dose-per-kg figure (commonly about 1 mg/kg), then caps the result near the usual adult maximum single dose of 50 mg.
How do I convert the dose to millilitres?
Divide the dose in milligrams by the liquid's concentration in mg/mL. A 20 mg dose with a 2.5 mg/mL syrup is 8 mL.
How often can it be taken?
Diphenhydramine is usually taken every 4 to 6 hours as needed, without exceeding the maximum total daily dose on the label.
Is this safe to use without a doctor?
No — this is an educational estimate only. Benadryl is not advised for young children without medical advice. Always confirm dosing with a pharmacist or doctor and follow the product label.