Lessons · Nursing · the metric ladder: g, mg, mcg, L, mL
The metric ladder: every rung is a thousand
Grams, milligrams and micrograms sit a thousand apart, and so do litres and millilitres: 1 g = 1000 mg, 1 mg = 1000 mcg, 1 L = 1000 mL. Going down a rung multiplies by a thousand; going up divides.
Hone is a place to practise a career, one idea a day. This is one of its lessons, written out in full and free to read without an account.
What it is for
The order says 0.25 mg and the tablets in the drawer say 250 mcg. Those are the same amount, and a nurse who cannot see that at 0600 with six patients waiting either gives one tablet and is right or gives a handful and is not. The decimal moves three places, and which way it moves is the whole question.
How to think about it
Say the two units out loud and decide which is bigger. Going from the bigger unit to the smaller one, the number gets bigger: multiply by 1000, decimal three places to the right. Going up, divide. Write the unit on the answer and check that a bigger unit came with a smaller number.
Worked example
1 g = 1000 mg; 1 mg = 1000 mcg; 1 L = 1000 mLThe ladder. Three rungs, a thousand between each pair.
0.5 g = 0.5 × 1000 = 500 mgDown a rung, so the number grows. Half a gram is five hundred milligrams.
250 mcg = 250 / 1000 = 0.25 mgUp a rung, so the number shrinks. Micrograms are the smallest unit on the ladder, so a dose in mcg looks big and is small.
1.5 L = 1.5 × 1000 = 1500 mLA bag and a half. The pump and the intake sheet both want millilitres.
Your turn
Write 0.75 g in milligrams.
0.75 g = mg
Solve one, graded on the server
The trap
Moving the decimal the wrong way. 0.25 mg written as 250 mg is a thousand times the dose, and the figure looks ordinary on the page. Ask which unit is bigger before you move anything, and write the unit down every time.