SR = Strength Required (what the prescriber ordered). SS = Strength of Stock (what you have on hand). The formula is always SR ÷ SS × Volume of Stock.

Can I split any tablet in half?

Only if the tablet is scored (has a line designed for splitting) and is not a modified-release, enteric-coated, or film-coated formulation. When in doubt, contact pharmacy before splitting.

The answer is 1.3 tablets — what do I do?

Query the prescription. Unusual fractional tablet doses often indicate a prescribing error, a wrong stock concentration, or a need to change to a different formulation. Do not round without clarifying.

Tablet & Oral Liquid Dose — Free Nurses Calculator

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Medication round, three patients in a row with different concentrations on the same drug. You need the draw-up volumes before you open a single blister pack.

Tablet & Oral Liquid Dose

Medication

Dose ordered — SR (mg)

Strength Required — prescribed

Stock strength — SS (mg)

mg per tablet or per stock mL

Stock volume

1 = tablet · 5 = 5 mL liquid

Form

Amount = (SR ÷ SS) × Stock volume Example: SR 750 mg, SS 500 mg tablet → (750÷500)×1 = 1.5 tablets
Liquid: SR 250 mg, SS 125 mg/5mL → (250÷125)×5 = 10 mL

💡 SUNRISE/SUNSET: Strength Required ÷ Stock Strength — applies to all drug calculations.

Reference: NPS MedicineWise · ACSQHC Medication Safety

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

1 What this calculator does

Calculates how many tablets to give, or how many mL to draw up for an oral liquid or injection, from a prescriber's order. Uses the SR ÷ SS × Volume formula — the universal nursing dose calculation.

2 Formula & professional reasoning

Volume to give = (Strength Required ÷ Strength of Stock) × Volume of Stock
  Tablets: Strength Required ÷ Strength of Stock (no volume component)

This formula works for every solid and liquid dose form. 'Strength Required' (SR) is what the prescriber ordered. 'Strength of Stock' (SS) is the concentration on the label of what you have. For liquids, you multiply by the volume in which that stock strength is dissolved. For tablets, if the answer is not a whole number or simple half, query the prescription — most tablets should not be split unless scored.

3 Worked examples

⚠️ Illustrative example only — not clinical or professional instruction.

Basic

Tablet dose — whole tablet

Given: Ordered: 500 mg · Stock: 500 mg/tablet

Working: 500 ÷ 500 × 1

Answer: 1 tablet

💡 Straightforward. Confirm tablet is the correct formulation (e.g. not slow-release).

Standard

Oral liquid — suspension

Given: Ordered: 250 mg · Stock: 125 mg / 5 mL

Working: 250 ÷ 125 × 5 = 2 × 5

Answer: 10 mL

💡 Use an oral syringe for accurate measurement. Shake suspension before measuring.

Advanced

Injection from ampoule

Given: Ordered: 75 mg morphine · Stock: 10 mg/mL

Working: 75 ÷ 10 × 1 = 7.5 mL

Answer: 7.5 mL

💡 Morphine 75 mg is above typical single-dose range — verify the prescription before drawing up. Two-nurse check required.

4 Sanity check

Tablet result check

Should be 0.5, 1, or 2 tablets for most drugs

Result > 2 tablets of same strength: query the prescription or check stock concentration.

Liquid result check

Should be between 1 mL and 20 mL for most oral doses

Under 1 mL is difficult to measure accurately. Over 20 mL is impractical — consider tablet form.

Injection result check

Usually 0.5–10 mL for most IM/IV doses

Over 10 mL for a single injection is unusual — verify before proceeding.

Mental cross-check

Result × SS = SR (always verify)

Multiply your answer by the stock strength — you should get back the ordered dose.

5 Common errors

Error	Cause	Consequence	Fix
Using the wrong stock concentration	Multiple strengths of same drug in the drug room	2× or 0.5× the ordered dose	Read the label every time. Do not rely on memory or colour of packaging.
Forgetting the volume component for liquids	Applying tablet formula to a liquid	Result in mg not mL — wrong unit	For liquids: always include the volume per stock strength (e.g. 5 mL in '125 mg/5 mL')
Calculating a half-tablet of a modified-release formulation	Result of 0.5 tablet on a non-scored or SR tablet	Dose dumping or unpredictable absorption	Modified-release and enteric-coated tablets must never be split — always check formulation type
Not verifying with a second nurse for high-alert drugs	Time pressure	Calculation errors go uncaught on narrow-therapeutic-index medications	Morphine, insulin, heparin, chemotherapy: mandatory independent double-check before every dose