Weight-Based Infusion Unit Conversion: mcg/kg/min and mL/hr

Practice unit conversion with fictional inputs

This is an educational spreadsheet exercise, not a validated medication calculator or a dosing protocol. It does not select a drug, starting dose, dosing weight, diluent, concentration, route or titration schedule. A real infusion requires the prescribed order, pharmacy preparation details, local protocol and independent professional checks.

The example values below are arbitrary arithmetic inputs. They must not be interpreted as a standard treatment for septic shock or any other condition.

Use final total volume for concentration

B2 is the supplied dose rate in mcg/kg/min; B3 is the specified dosing weight in kg; B4 is the total drug amount in mg; B5 is the final total solution volume in mL. It is not necessarily the volume of diluent added. Match the drug-amount basis on the preparation label; salt/base conventions cannot be resolved by this formula.

B10 computes concentration as B4 × 1000 / B5. For the fictional 4 mg and final 250 mL, it is 16 mcg/mL. The 1000 converts milligrams to micrograms.

=IF(B8<>"OK",B8,B4*1000/B5)

Validate before either direction of conversion

B8 requires four numeric entries, nonnegative dose rate and strictly positive weight, drug amount and final volume. A blank dose must not silently become zero. A deliberate zero dose is accepted mathematically, but is not advice to stop an infusion.

=IF(COUNT(B2:B5)<>4,"Complete numeric inputs",IF(OR(B2<0,B3<=0,B4<=0,B5<=0),"Check input ranges","OK"))

Convert dose rate to volumetric rate

Multiplying mcg/kg/min by kg and 60 min/hour gives mcg/hour. Dividing by mcg/mL leaves mL/hour. B11 is 30 for B2=0.1, B3=80 and concentration 16. Changing only B2 to 0.25 gives 75. Then doubling the drug amount B4 to 8 gives 37.5.

Keep B10 and B11 unrounded internally. A display format does not determine a device’s permitted rate increments. Any operational rounding must follow the device and clinical protocol, not an arbitrary two-decimal rule.

=IF(B8<>"OK",B8,B2*B3*60/B10)

Enter a separate rate for the reverse calculation

B6 is an independently entered rate in mL/hour. B12 converts that rate and the stated concentration back to mcg/kg/min. With B6=30 and the initial preparation, B12 is 0.1. B13 is the signed difference between reconstructed and supplied dose rates.

If only B6 changes to 15, the reconstructed dose becomes 0.05 and the difference −0.05. B6 is deliberately not a formula linked to B11: a linked round-trip would always agree and would not test an independently entered value.

=IF(B8<>"OK",B8,IF(NOT(ISNUMBER(B6)),"Check rate input",IF(B6<0,"Check rate input",B6*B10/(B3*60))))

Understand what agreement does not prove

A zero arithmetic difference is not proof that a real pump, preparation or order is correct. Both calculations can share the same wrong weight, concentration or units. The spreadsheet does not read or control a pump, verify a label or detect a clinically inappropriate dose.

Try doubling final volume at constant drug amount: concentration halves and the calculated volumetric rate doubles. Doubling the drug amount at constant volume has the opposite effect. Erase any required core input or enter a negative number to inspect the validation messages.

Further reading

• NHS SORT — Infusion calculations and total-volume concentration
• NHS Highland — Noradrenaline formulary, rate-to-dose calculation