This is the whole thing. Each step is 1000. Nothing else to know.
kgkilogram
×1000 → ← ÷1000
ggram
×1000 → ← ÷1000
mgmilligram
×1000 → ← ÷1000
mcgmicrogram
The only rule you need: going DOWN the ladder to a smaller unit, the number gets
BIGGER — multiply by 1000, move the decimal 3 places right.
Going UP to a bigger unit, the number gets SMALLER — divide by 1000, decimal 3 places left.
Conversion
Equals
Worked example
1 kg
1000 g
2.5 kg = 2500 g
1 g
1000 mg
0.5 g = 500 mg
1 mg
1000 mcg
0.25 mg = 250 mcg
1 g
1,000,000 mcg
rarely asked, but true
1 L
1000 mL
1.5 L = 1500 mL
1 mL
1 cc
identical — 30 mL = 30 cc
1 grain (gr)
60 mg
gr 1/2 = 30 mg · older orders only
🥤 Household volume → mL
Liquid medications and intake & output. These are the ones that show up over and over.
Household
=
Also equals
Where it shows up
1 tsp
5 mL
—
Liquid antibiotics, cough syrup
1 tbsp
15 mL
3 tsp
Antacids, laxatives
1 fluid ounce (oz)
30 mL
2 tbsp · 6 tsp
Med cups, I&O, tube flushes
1 teacup
180 mL
6 oz
I&O trays
1 cup / glass
240 mL
8 oz · 16 tbsp
I&O, fluid restriction teaching
1 pint
480 mL
2 cups · 16 oz
Blood products, bowel prep
1 quart
960 mL
2 pints · 4 cups · 32 oz
Roughly 1 liter
1 gallon
3840 mL
4 quarts · 128 oz
Colonoscopy prep
The chain that unlocks most questions: 1 tsp = 5 mL → 3 tsp = 1 tbsp = 15 mL
→ 2 tbsp = 1 oz = 30 mL → 8 oz = 1 cup = 240 mL. If you only memorize one line on this page, memorize that one.
⚖️ Body weight — lb ↔ kg
Conversion
Equals
Direction
1 kg
2.2 lb
lb → kg: DIVIDE by 2.2
1 lb
0.45 kg
kg → lb: MULTIPLY by 2.2
1 lb
16 oz (weight)
Newborn weights
1 oz (weight)
about 30 g
Newborn weights
Sanity check: kilograms are always the SMALLER number. A 200 lb client is about 90 kg.
If your kg answer is bigger than the lb you started with, you multiplied when you should have divided.
Weight-based orders: convert the weight to kg FIRST, before you touch the dose.
Doing it in the wrong order is the single most common weight-based math error.
🎯 The short list to memorize
Everything else on this page can be built from these ten.
1 kg = 1000 g
metric
1 g = 1000 mg
metric
1 mg = 1000 mcg
metric
1 L = 1000 mL
metric
1 tsp = 5 mL
household
1 tbsp = 15 mL
= 3 tsp
1 oz = 30 mL
= 2 tbsp
1 cup = 240 mL
= 8 oz
1 kg = 2.2 lb
body weight
1 mL = 1 cc
same thing
🧠 How to set it up so you stop guessing
1. The formula for "how much do I give?"
(Desired ÷ Have) × Quantity = amount to give
Desired = what the order says. Have = the strength on the label.
Quantity = the volume or tablets that strength comes in.
Order
Label says
Set-up
Answer
metoprolol 50 mg
25 mg tablets
(50 ÷ 25) × 1 tab
2 tablets
amoxicillin 500 mg
250 mg per 5 mL
(500 ÷ 250) × 5 mL
10 mL
furosemide 30 mg
40 mg per 4 mL
(30 ÷ 40) × 4 mL
3 mL
2. Convert BEFORE you divide
The formula only works when Desired and Have are in the same unit.
If the order says grams and the bottle says milligrams, fix that first. This is where most wrong answers come from.
Half a tablet, 2 tablets, 5–15 mL of a liquid: reasonable.
38 tablets or 0.006 mL: you slipped a decimal. On a test, an answer that is off by exactly 1000
almost always means a mg/mcg mix-up.
🚨 The traps they write questions about
Fluid ounce is NOT weight ounce. 1 fluid oz = 30 mL (volume).
1 weight oz = about 30 g (mass). Same word, different measurement. Read whether the question is about
liquid the client drank or how much something weighs.
mg vs mcg is a 1000-fold error. This is the classic fatal medication error.
Digoxin, levothyroxine and fentanyl are commonly ordered in mcg. Slow down whenever both units appear in one problem.
Leading zero YES, trailing zero NO. Write 0.5 mg, never .5 mg — the dot gets
missed and it reads as 5 mg. Write 5 mg, never 5.0 mg — that reads as 50 mg.
This is a test question, not just a style note.
Never abbreviate "units." Write out units. A "U" mistaken for a zero has caused
10-fold insulin overdoses. Same for "international units" — spell it out.
Household measuring is imprecise. Teach clients to use the dosing syringe or the
cup that came with the medication, never a kitchen teaspoon. A kitchen "teaspoon" ranges from about 3 to 7 mL.
Rounding: follow whatever your course says. In general, tablets round to the nearest
half or whole, mL for adults to the nearest tenth, and IV pump rates to the nearest whole mL/hr.
💉 IV rate math
What you want
Formula
Example
mL per hour
total mL ÷ total hours
1000 mL over 8 hr = 125 mL/hr
gtt per minute
(mL × drop factor) ÷ minutes
1000 mL, 15 gtt/mL, 480 min = 31 gtt/min
Microdrip shortcut
60 gtt/mL → gtt/min = mL/hr
80 mL/hr = 80 gtt/min
Infusion time
total mL ÷ mL per hour
500 mL at 125 mL/hr = 4 hours
Drop factors: macrodrip sets are 10, 15 or 20 gtt/mL — the number is
printed on the tubing package. Microdrip is always 60 gtt/mL. Drops per minute always round to a whole number.
✏️ Practice — work it, then open it
Do it on paper first. The answer shows every step, not just the number.
1. Order: 0.75 g PO. Available: 250 mg tablets. How many tablets?
3 tablets
g -> mg is a SMALLER unit, so multiply by 1000
0.75 g x 1000 = 750 mg
750 mg / 250 mg per tab = 3 tablets
2. Order: 500 mcg. Available: 0.25 mg tablets. How many tablets?
2 tablets
Get both into the same unit first.
500 mcg / 1000 = 0.5 mg
0.5 mg / 0.25 mg per tab = 2 tablets
3. The provider orders 2 tablespoons of a liquid antacid. How many mL?
30 mL
1 tbsp = 15 mL
2 x 15 = 30 mL (also = 1 fluid ounce)
4. A client drank 1 cup of coffee, 6 oz of juice and 240 mL of water. Total intake in mL?
660 mL
1 cup = 240 mL
6 oz x 30 = 180 mL
water = 240 mL
240 + 180 + 240 = 660 mL
5. A client weighs 176 lb. What is the weight in kg?
80 kg
1 kg = 2.2 lb, so DIVIDE by 2.2
176 / 2.2 = 80 kg
6. Order: 15 mg/kg for a client weighing 44 lb. How many mg?
300 mg
Convert the weight FIRST.
44 / 2.2 = 20 kg
20 kg x 15 mg/kg = 300 mg
7. Order: amoxicillin 375 mg PO. Available: 250 mg per 5 mL. How many mL? How many tsp?
7.5 mL = 1.5 tsp
Desired / Have x Quantity
375 / 250 x 5 = 7.5 mL
7.5 / 5 = 1.5 tsp
8. Convert 0.04 mg to mcg.
40 mcg
mg -> mcg is SMALLER, so multiply by 1000
0.04 x 1000 = 40 mcg
(decimal hops 3 places RIGHT)
9. A client is to drink 1.5 L of fluid per day. How many 8 oz cups is that?
About 6 cups
1.5 L = 1500 mL
1 cup = 8 oz = 240 mL
1500 / 240 = 6.25, so about 6 cups
10. Infuse 1000 mL over 8 hours. What is the rate in mL/hr?
125 mL/hr
Total volume / total hours
1000 / 8 = 125 mL/hr
11. A child weighing 33 lb is ordered 5 mg/kg/day divided into 3 doses. How many mg per dose?
25 mg per dose
33 / 2.2 = 15 kg
15 x 5 = 75 mg per DAY
75 / 3 doses = 25 mg per dose
12. Available: 1 gram in 50 mL. The order is 400 mg. How many mL?