Practice mg/kg/day to mg per Dose and mL Conversions

Use fictional values to learn the units

This is a dimensional-arithmetic exercise, not a pediatric prescription calculator. No medicine or indication is specified. The numbers 45 mg/kg/day, 1000 mg/day and 400 mg per 5 mL are hypothetical inputs, not recommended doses or a universal adult maximum.

A clinician or pharmacist must establish the appropriate regimen, weight basis, frequency, maximum and formulation for an actual patient. A MIN formula cannot evaluate age restrictions, renal or hepatic function, interactions, allergies, obesity dosing or whether a drug is appropriate.

Read the regimen carefully: mg/kg/day means a total for the day, whereas mg/kg/dose means an amount for each administration. This worksheet supports only the former with equal-sized doses. Entering a per-dose regimen as a daily regimen would calculate the wrong amount.

Inputs and units

Use numeric values in the listed units. Pounds must first be converted to kilograms. The daily cap must be in mg per day, not mg per administration. If a prescribed regimen also has a per-dose maximum, that separate constraint is not modeled here.

Apply the supplied daily cap

E2 calculates MIN(B5,B2×B3). Initially 18×45=810 mg/day, below the hypothetical 1000 mg/day cap. E5 tells you whether the cap changes the calculated daily total.

Changing the fictional weight to 32 kg gives an uncapped total of 1440 mg/day; the formula then returns 1000. This proves only that the supplied numerical limit is enforced, not that the resulting amount is safe for any medicine.

=IF(COUNT(B2:B7)<>6,"Complete numeric inputs",IF(OR(B2<=0,B3<=0,B4<=0,B5<=0,B6<=0,B7<=0,B4<>INT(B4)),"Require positive inputs and whole doses per day",MIN(B5,B2*B3)))

Divide into equal amounts

E3 divides the capped daily amount by B4. With two equal doses, 810/2=405 mg per dose. A daily count does not by itself establish administration times or intervals; those come from the actual instructions.

=IF(COUNT(B2:B7)<>6,"Complete numeric inputs",IF(OR(B2<=0,B3<=0,B4<=0,B5<=0,B6<=0,B7<=0,B4<>INT(B4)),"Require positive inputs and whole doses per day",MIN(B5,B2*B3)/B4))

Convert mass to volume without premature rounding

B6/B7 is concentration in mg/mL. For the fictional ratio 400 mg per 5 mL, concentration is 80 mg/mL. E4 calculates 405/80=5.0625 mL. It preserves the mathematical result rather than declaring a two-decimal amount suitable for an oral syringe.

The actual measurable amount and rounding must be verified against the prescribed instructions, formulation and dosing device. Use mL consistently with an appropriately marked device; do not translate the result into household spoonfuls.

With the capped fictional daily total of 1000 and two equal doses, E3 is 500 mg and E4 is 6.25 mL. Doubling the concentration halves calculated volume while leaving the mass unchanged.

=IF(COUNT(B2:B7)<>6,"Complete numeric inputs",IF(OR(B2<=0,B3<=0,B4<=0,B5<=0,B6<=0,B7<=0,B4<>INT(B4)),"Require positive inputs and whole doses per day",(MIN(B5,B2*B3)/B4)*B7/B6))

Check missing values and changed concentrations

Clear the concentration or enter zero doses per day: the worksheet reports invalid or incomplete inputs, rather than dividing by zero. Fractional dose counts are rejected because this simplified exercise assumes a whole number of equal daily doses.

Try 800 mg per 10 mL: it is the same concentration as 400 mg per 5 mL, so volume must stay the same. Entering the wrong strength from another bottle is a data error that numeric validation cannot detect.

Further reading

• Pediatric Pharmacy Association — Medication Dosing for Children With Overweight and Obesity
• FDA — Safe Use Initiative: oral liquid medication dosing designations
• American Academy of Pediatrics — Metric Units and the Preferred Dosing of Orally Administered Liquid Medications