A dosage calculator that shows every method
For healthcare professionals and students. Check results against your local protocols and clinical judgement; this tool does not give medical advice. It is not for self-treatment and has no drug list or default doses.
This dosage calculator works the classic nursing dosage calculation formula — desired over have times quantity, D/H × Q — and shows the same answer by dimensional analysis and by ratio and proportion, so you can check your own method against it. It converts between grams, milligrams and micrograms, caps the amount at a maximum single dose you enter, and rounds to what you can actually measure without ever rounding above that maximum.
A second mode generates dosage calculation practice questions: tablets, liquids and injections, weight-based mg/kg doses with pound-to-kilogram conversion and dose limits, and IV pump and gravity rates. Every question has a worked answer, and a set number makes a set repeatable for a class or a study group.
How to use the Dosage Calculator (D/H × Q) with Practice Questions
- Enter the Desired dose (D) from the order and pick its unit.
- Enter the Dose on hand (H) from the label — the drug in one tablet or capsule, or in the volume — and its unit.
- Enter the Quantity (Q): 1 tablet or capsule, or the mL that contain H (5 for “250 mg per 5 mL”).
- Optionally add a maximum single dose and a rounding step. Read the amount, the warnings and the three methods of working.
- For practice, switch to Practice questions, choose how many and which kinds, answer each one and press Check.
Dosage Calculator (D/H × Q) with Practice Questions features
Three methods, one answer
Formula method, dimensional analysis chain and ratio–proportion are printed with your numbers.
Unit conversion built in
g, mg and mcg convert automatically; units, mmol and mEq must match between order and stock.
Maximum-dose cap
An order above the maximum is worked for the maximum and flagged for clarification; rounding never exceeds it.
Measurability checks
Flags tablets that are not whole or half, split capsules, more than three tablets, tiny or very large volumes and likely mg/mcg mix-ups.
Seeded practice sets
Generated questions with clean numbers, worked answers and instant marking; the same set number gives the same set on any device.
The dosage calculation formula and dimensional analysis
The formula method is amount = D ÷ H × Q: what is desired, divided by what you have, multiplied by the quantity the “have” comes in. D and H must be in the same unit first, which is where most errors happen — 1 g = 1,000 mg and 1 mg = 1,000 mcg.
Worked example (made-up numbers): 1 g is ordered and the tablets are 500 mg. Convert: 1 g = 1,000 mg. Then 1,000 ÷ 500 × 1 tablet = 2 tablets. By dimensional analysis the units cancel along a chain: 1 g × (1,000 mg / 1 g) × (1 tablet / 500 mg) = 2 tablets. By ratio and proportion, 500 mg : 1 tablet = 1,000 mg : x, so x = 2.
For a liquid, 375 mg ordered with 250 mg per 5 mL on hand gives 375 ÷ 250 × 5 = 7.5 mL. If a maximum of 300 mg applied, the calculator would work 300 ÷ 250 × 5 = 6 mL and tell you to clarify the order before giving anything.
Practice question types
An answer is marked correct when it is within half of the last decimal place asked for, so both the rounded and the exact value count. Course rules differ — some round only at the end, some use 2.2 and others 2.205 lb per kg — so follow your programme’s rules in exams.
| Kind | What it trains | Rounding |
|---|---|---|
| Tablets | D/H × Q with g → mg and mg → mcg conversions | Nearest half tablet |
| Liquids and injections | mg to mL from “mg per 5 mL” and “mg per mL” strengths | 0.1 mL |
| Weight-based | mg/kg per dose or per day in divided doses, lb → kg (2.2 lb = 1 kg) and a per-dose limit | 0.1 mL, never above the limit |
| IV rates | mL/h on a pump and drops/min with 10, 15, 20 or 60 drops/mL sets | Whole numbers |
Limits
- It checks arithmetic, not appropriateness: it cannot tell whether a dose suits the patient, the route or the indication. Check safe dose ranges in your formulary.
- Weight-based doses with daily caps are handled in more detail by the mg/kg medicine dose calculator; volume-from-concentration problems by the mg to mL calculator; infusions by the drip rate calculator.
- Practice numbers are generated, not taken from real products, and no question names a medicine.
Dosage Calculator (D/H × Q) with Practice Questions FAQ
What is the dosage calculation formula?
Desired dose divided by the dose on hand, multiplied by the quantity: D ÷ H × Q. Convert D and H to the same unit first. For 1 g ordered and 500 mg tablets: 1,000 ÷ 500 × 1 = 2 tablets.
How do I do dosage calculation by dimensional analysis?
Start with the ordered amount and multiply by conversion factors written as fractions so each unwanted unit cancels, ending in the unit you give: 375 mg × (5 mL / 250 mg) = 7.5 mL.
Is this dosage calculator for nursing students?
Yes — it shows the working the way nursing courses teach it, and the practice mode gives unlimited questions with worked answers. Clinicians can use it to double-check, following local policy.
Why does it say my tablet dose can’t be measured?
Tablets are normally split only in half and only when scored, and capsules cannot be split. An answer like 0.4 tablets usually means a wrong unit or strength.
What happens when the order is above the maximum dose?
The amount is worked for the maximum you entered and a warning tells you to clarify the order with the prescriber before giving anything.
Can I get the same practice questions again?
Yes. Each set has a number; type it into Set number to get exactly the same questions, which is handy for a class.