Liquid Medication and Injection Dosage Calculator (mL)
Calculate how many mL to give for oral liquids and injections with desired over have × quantity, and the right rounding for the syringe.
Formula
mL = desired dose ÷ dose on hand × volume on hand (mL)
D ÷ H × Q
How to calculate it step by step
- Read the concentration on the label: the drug amount (H) in a volume (Q), for example 250 mg per 5 mL or 10 mg/mL.
- Convert the order to the same unit as the label if needed.
- Divide the desired dose by the dose on hand, then multiply by the volume.
- Round to the tenth of a mL if the answer is 1 mL or more, to the hundredth if it is less than 1 mL.
- Choose a syringe that measures that amount: a 1 mL syringe for volumes under 1 mL, an oral syringe for oral liquids.
Worked examples
Example 1. Order: ibuprofen 150 mg PO. Available: ibuprofen oral suspension 100 mg per 5 mL. How many mL will you give?
- mL = desired ÷ have × quantity = 150 ÷ 100 × 5 mL = 7.5 mL.
- Round to the tenth: 7.5 mL.
Answer: 7.5 mL
Example 2. Order: furosemide 20 mg IV push. Available: furosemide injection 10 mg/mL. How many mL will you draw up?
- mL = desired ÷ have × quantity = 20 ÷ 10 × 1 mL = 2 mL.
- Round to the tenth: 2 mL.
Answer: 2 mL
Rounding
Volumes of 1 mL or more are rounded to the tenth; volumes under 1 mL are rounded to the hundredth and drawn up in a 1 mL syringe. Always keep the leading zero (0.5 mL, never .5 mL).
Common mistakes
- Forgetting the quantity: 375 mg of a 250 mg/5 mL suspension is 375 ÷ 250 × 5 = 7.5 mL, not 1.5 mL.
- Using the total volume of the vial instead of the concentration per mL.
- Writing a trailing zero (5.0 mL) that can be misread as 50 mL.
Nursing safety points
- Measure oral liquids with an oral syringe or a calibrated cup, never a kitchen spoon.
- Check the maximum volume for the route: most adult IM sites take up to 3 mL (deltoid about 1 mL), subcutaneous injections usually up to 1 mL.
- For IV push, check how long to push the drug over and whether it must be diluted.
Frequently asked questions
How do you calculate mL for a liquid medication?
mL = desired ÷ have × volume. For amoxicillin 500 mg with a 250 mg/5 mL suspension: 500 ÷ 250 × 5 = 10 mL.
How do you round mL for an injection?
If the volume is 1 mL or more, round to the tenth (for example 1.3 mL). If it is less than 1 mL, round to the hundredth and use a 1 mL syringe (for example 0.25 mL).
How many mL of morphine 4 mg/mL for a 2 mg dose?
2 mg ÷ 4 mg × 1 mL = 0.5 mL.