Overview

Unit conversion is the first step of nearly every dosage calculation: the prescriber writes one unit and the pharmacy supplies another, and no formula works until both sides match. The metric ladder moves in steps of 1,000 — 1 g = 1,000 mg and 1 mg = 1,000 mcg — and volume follows the same pattern with 1 L = 1,000 mL. Two other equivalences appear constantly on the floor: 1 mL equals 1 cc, and 1 kg equals 2.2 lb. Because the metric steps are thousand-fold, a conversion done in the wrong direction is not a small error; it is a thousand times the intended dose.

Interpretation

1 g = 1,000 mg Hallmarkx1,000

1 mg = 1,000 mcg Hallmarkx1,000

1 L = 1,000 mL Hallmarkx1,000

1 kg = 2.2 lb Hallmarkx2.2

the one everyday factor that is not a thousand

1 mL = 1 cc

the same volume named two ways, not a conversion

1 tsp = 5 mL

1 tbsp = 15 mL

1 oz = 30 mL

Technique

Worked conversion: 0.5 g ordered, 250 mg tablets supplied

Name both unitsorder in g, supply in mg
Pick the directiong to mg is a smaller unit
Multiply by 1,0000.5 x 1,000 = 500 mg
Sanity-checkthe number got bigger, as it should
Then calculate500 / 250 = 2 tablets

During — Monitoring

Compare the converted number with the original Hallmark

wrong direction shows up as a thousand-fold difference

Ask whether the final dose is a plausible number of tablets or millilitres Hallmark

Have a second nurse check high-alert conversions

Use a leading zero and never a trailing zero

0.5 mg, not .5 mg or 0.50 mg

Patient Teaching

Use the dosing syringe or cup, never a kitchen spoon Hallmark

a household teaspoon is not 5 mL

Read the label unit as well as the number

Ask the pharmacist if the label unit differs from the prescription

Do not convert doses at home from an internet chart

Report Nowescalate immediately

An answer that is 1,000 times bigger or smaller than expected Hallmark

the conversion went the wrong way

A dose requiring an implausible number of tablets Hallmark

A prescription written with a trailing zero

5.0 mg reads as 50 mg if the point is missed

A prescription with no leading zero

.5 mg reads as 5 mg

Order and supply units that never got reconciled

Clinical Pearl

Smaller unit, bigger number. If you converted grams to milligrams and the number got smaller, you divided when you should have multiplied.

Unit Conversion

Overview

Interpretation

Technique

During — Monitoring

Patient Teaching

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