The ladder: every conversion the exam will hand you
A staircase descending left to right with treads labeled kg, g, mg, mcg and an offset two-tread flight for L and mL, each riser carrying a multiply-by-1000 down arrow and a divide-by-1000 up arrow, with a separate ramp at a different angle joining pounds to kilograms.
The equalities
| Equality | Equality | |
|---|---|---|
| 1 kg = 1000 g | 1 L = 1000 mL | |
| 1 g = 1000 mg | 1 kg = 2.2 lb | |
| 1 mg = 1000 mcg | 1 tsp = 5 mL | |
| 1 tbsp = 15 mL |
Seven equalities. Nothing else is memorized. Everything the exam asks is built from these.
The direction rule
Larger unit to smaller unit, the number gets bigger. Smaller unit to larger unit, the number gets smaller. If your answer moved the wrong way, you divided where you should have multiplied. Check the direction before you check the digits.
Six worked conversions
0.35 g × (1000 mg / 1 g) = 350 mg
1250 mcg × (1 mg / 1000 mcg) = 1.25 mg
2.5 L × (1000 mL / 1 L) = 2500 mL
44 lb × (1 kg / 2.2 lb) = 20 kg
0.4 mg × (1000 mcg / 1 mg) = 400 mcg
2 tsp × (5 mL / 1 tsp) = 10 mL
One more on the pound ramp
A charted weight of 187 lb. 187 lb × (1 kg / 2.2 lb) = 85 kg. Check the direction: kilograms are the larger unit, so the number should shrink, and 85 is smaller than 187. The direction rule passed before the arithmetic was reviewed.
The pound gate
Every weight-based order in this book, and every weight-based order on the exam, is written per kilogram. Charted weights are frequently in pounds. The conversion is not a step inside the problem. It is the gate the problem sits behind, and a problem worked past a closed gate is wrong no matter how clean the rest of the setup looks.
Watch outWEIGHT UNITS. The weight is the trap, not the drug. → BOOK 06 · P9
Margin notemicrograms are written mcg, never with a Greek symbol.
Takeawayseven equalities and one direction rule cover every conversion the exam asks for.