Why do I add diluent first?

Drawing diluent into the syringe first allows you to see the volume clearly, reduces aeration risk, and makes it easier for a second nurse to verify the drug volume when it is added.

What diluent should I use?

Check the drug monograph — most drugs use 0.9% NaCl (normal saline) or 5% Dextrose. Some drugs (e.g. amphotericin) require specific diluents. Never assume compatibility without checking.

Can I prepare IV admixtures on the ward?

In Australia and the US, complex IV admixtures should ideally be prepared by pharmacy under aseptic conditions. Ward-level preparation is acceptable for urgent bolus and syringe driver preparations following strict aseptic non-touch technique (ANTT).

Drug Dilution Calculator — Free Nurses Calculator

🎯

You need a morphine infusion at 1 mg/mL but the ampoule is 15 mg/mL. The pump rate is set — now you need the right diluent volume to reach the target concentration.

Drug Dilution Calculator

Dilution

Drug required (mg)

Stock concentration (mg/mL)

Target final volume (mL)

Target concentration (mg/mL)

Stock drawn = Drug required ÷ Stock concentration Diluent = Final volume − Stock drawn Example (morphine): 30 mg needed, stock 10 mg/mL, final 30 mL
Stock = 3 mL · Diluent = 27 mL saline

Reference: NCBI Nursing Skills Ch.5 · NPS MedicineWise

⚕️ Clinical safety: 🇦🇺 Verify with facility drug formulary and senior clinician · Meets AHPRA/ACSQHC standards

1 What this calculator does

Calculates how much diluent to add to achieve a target concentration from a stock solution. Used for preparing morphine, heparin, potassium and other drugs that must be diluted before IV administration. Uses the C1V1 = C2V2 dilution formula.

2 Formula & professional reasoning

Diluent to add (mL) = Final volume − Drug volume
Drug volume = (C2 × V2) ÷ C1
Where C1=stock concentration, C2=target concentration, V2=final volume

The C1V1 = C2V2 relationship (stock concentration × stock volume = final concentration × final volume) is the foundation of all dilution calculations. The drug volume is calculated first, then the diluent volume is simply the difference between desired final volume and drug volume. Always prepare in a suitable diluent (0.9% NaCl or 5% Dextrose as directed by the drug monograph).

3 Worked examples

⚠️ Illustrative example only — not clinical or professional instruction.

Basic

Morphine syringe driver

Given: Stock: 15 mg/mL · Target: 1 mg/mL · Final volume: 30 mL

Working: Drug vol: (1 × 30) ÷ 15 = 2 mL · Diluent: 30 − 2

Answer: 2 mL morphine + 28 mL NaCl 0.9%

💡 Draw up diluent first, then add morphine. Label with drug, concentration, date/time, nurse signature.

Standard

Heparin infusion

Given: Stock: 1000 units/mL · Target: 25 units/mL · Final volume: 50 mL

Working: Drug vol: (25 × 50) ÷ 1000 = 1.25 mL · Diluent: 50 − 1.25

Answer: 1.25 mL heparin + 48.75 mL NaCl 0.9%

💡 Heparin is a high-alert medication. Two-nurse independent check mandatory before preparation and administration.

Advanced

Potassium chloride correction

Given: Stock: 2 mmol/mL · Target: 0.1 mmol/mL · Final volume: 100 mL

Working: Drug vol: (0.1 × 100) ÷ 2 = 5 mL · Diluent: 100 − 5

Answer: 5 mL KCl + 95 mL NaCl 0.9%

💡 ⚠️ KCl is a VERY high-alert medication. Must be administered via infusion pump. Never give undiluted. Concentration must not exceed 0.1 mmol/mL peripherally.

4 Sanity check

Drug volume should be much less than final volume

Drug vol typically 1–20% of final volume

If drug volume is > 50% of final volume, consider a more concentrated stock or smaller final volume.

KCl peripheral limit

≤ 0.1 mmol/mL peripheral; ≤ 0.4 mmol/mL central

Concentrated potassium given peripherally causes phlebitis and cardiac risk.

Morphine concentration check

Typical: 1–5 mg/mL for continuous infusion

Concentrations >5 mg/mL are considered high concentration — extra caution required.

Always label the prepared syringe

Drug · Concentration · Volume · Date/time · Prepared by

Unlabelled syringes must never be used.

5 Common errors

Error	Cause	Consequence	Fix
Adding drug to an empty syringe then adding diluent (aeration risk)	Incorrect order of preparation	Micro-air emboli risk; also calculation verification harder	Draw diluent into syringe first, then add the calculated drug volume
Calculating diluent as the final volume, not the make-up volume	Confusing final volume with diluent volume	Final concentration higher than intended	Diluent to ADD = Final volume MINUS drug volume — not equal to final volume
Using wrong diluent	Defaulting to available diluent without checking	Drug incompatibility, precipitation	Always check the drug monograph (AMH/Micromedex) for the recommended diluent for each drug
Skipping two-nurse check for high-alert drugs	Preparation done alone	Dilution errors in morphine, heparin, KCl can be fatal	All high-alert IV preparations require a second independent nurse to verify calculation and preparation