Percent and Ratio Solution Calculator (mg/mL)
Convert solution strengths given as a percent (2% lidocaine, D5W, 50% magnesium sulfate) or a ratio (1:1,000) to mg/mL, and find how much drug is in a volume.
Formula
X% solution = X g per 100 mL = X × 10 mg/mL
1:Y solution = 1 g in Y mL = 1,000 ÷ Y mg/mL
How to calculate it step by step
- For a percent: the number is grams per 100 mL. Multiply by 10 to get mg/mL.
- For a ratio 1:Y: 1 g is in Y mL. Divide 1,000 mg by Y to get mg/mL.
- Multiply mg/mL by the volume to find the amount of drug in that volume.
Worked examples
Example 1. How many grams of dextrose are in 500 mL of D5W?
- D5W is 5% dextrose: 5 g per 100 mL.
- 500 mL × 5 g ÷ 100 mL = 25 g.
Answer: 25 g
Example 2. Epinephrine 1:1,000. How many mg are in 1 mL?
- 1:1,000 means 1 g in 1,000 mL.
- 1,000 mg ÷ 1,000 mL = 1 mg/mL.
Answer: 1 mg
Rounding
Keep full precision for concentrations; round the final volume or amount as for any dose.
Common mistakes
- Treating 2% as 2 mg/mL: it is 2 g per 100 mL, so 20 mg/mL.
- Confusing epinephrine 1:1,000 (1 mg/mL) with 1:10,000 (0.1 mg/mL), a tenfold error.
Nursing safety points
- Since 2016, US epinephrine labels show the strength in mg/mL instead of a ratio. Read the mg/mL on the label.
- Concentrated electrolytes (potassium chloride, 50% magnesium sulfate, hypertonic saline) are high-alert medications and must be diluted as directed.
Frequently asked questions
How many mg/mL is 2% lidocaine?
2% = 2 g per 100 mL = 2,000 mg ÷ 100 mL = 20 mg/mL.
How many grams of dextrose are in 1 L of D5W?
D5W is 5 g per 100 mL, so 1,000 mL contains 50 g.
What does epinephrine 1:1,000 mean?
1 g in 1,000 mL, which is 1 mg/mL.