MedMaths Calculation Guides
Plain-English medication maths and clinical calculation Guides with worked methods, limitations, safety context and references.
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Calculation guide
How to Read Medication Labels and Concentrations
Learn how to identify the exact current medication product, dosage form and strength basis, separate total amount/total volume from per-mL concentration, and stop when prepared-label information is missing or unclear.
Formula explainer
IV drip rates explained: drop factor, gtt/min and common errors
Understand what the drop factor means, why gtt/mL and gtt/min are different, how gravity flow relates to mL/hr, and where calculation errors happen.
Formula comparison
Pediatric maintenance fluids explained: 4-2-1 vs 100-50-20
100-50-20 is the Holliday-Segar daily maintenance method; 4-2-1 is a rounded hourly shortcut based on the same weight bands. This guide explains the relationship, why the totals can differ, and the clinical limits of full maintenance.
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Medication Calculations
3Dose, tablet, weight-based and medication-unit calculations.
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Medication Calculations
3Dose, tablet, weight-based and medication-unit calculations.
Calculation guide
Medication Units and Units/mL Explained
Understand medication units, units/mL concentration, units-to-volume and hourly-rate relationships, insulin concentration/device boundaries, and common units-based errors.
Calculation guide
Weight-Based Medication Dosing: mg/kg to mL Explained
Learn pediatric and paediatric weight-based medication dosing from a verified mg/kg order to liquid volume, including per-dose vs per-day orders, divided doses, current kilograms, concentration and safety checks.
Calculation guide
Tablet Dose Calculations Explained: Formula & Worked Examples
Understand D/H × Q, what Q really means, how to match units, how per-dose and daily-total orders differ, and why fractional tablet or non-whole capsule results need a separate product-specific check.
Medication Preparation
6Labels, volumes, reconstitution, concentration and dilution.
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Medication Preparation
6Labels, volumes, reconstitution, concentration and dilution.
Formula comparison
Reconstitution vs dilution: what's the difference?
Separate reconstitution from dilution, understand where final volume and concentration come from, and choose the right MedMaths calculation without mixing preparation stages.
Calculation guide
How to Read a Medication Syringe in mL
A step-by-step guide to reading mL syringe graduations, finding the value of each small mark, matching a known mL target to the scale, and recognizing when device type or syringe size matters.
Calculation guide
How to Read Medication Labels and Concentrations
Learn how to identify the exact current medication product, dosage form and strength basis, separate total amount/total volume from per-mL concentration, and stop when prepared-label information is missing or unclear.
Calculation guide
What Percentage Strength Means on a Medication Label
A percentage on a label is a concentration meaning an amount per 100. This Guide covers what w/v, v/v and w/w each measure, and how to turn a % w/v strength into mg/mL.
Formula explainer
C₁V₁ = C₂V₂ Explained for Medication Dilution
Learn how C₁V₁ = C₂V₂ works for medication dilution, what each value means, how to read dilute-to versus dilute-with wording, and where product-specific preparation rules begin.
Methodology
Medication Reconstitution Explained
Learn how to calculate from a reconstituted medication, use a stated concentration, distinguish diluent from final volume, handle solution-versus-suspension concepts, and verify product-specific preparation context.
Medication Safety & Foundations
7Units, rounding, reasonableness, dose limits and safe administration.
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Medication Safety & Foundations
7Units, rounding, reasonableness, dose limits and safe administration.
Calculation guide
Medication Maths Unit Conversions Explained
Learn medication math unit conversions for mass, volume and time, safe decimal and microgram notation, source-supplied kg/lb conversion, and why mg to mL or medication units need product-specific information rather than a universal conversion.
Calculation guide
How to Read a Medication Maths Question
Learn how to decode medication maths and dosage calculation word problems using the current order, verified product, exact target, matching units and a STEP when the problem is multi-stage.
Methodology
Medication Calculation Methods Explained
Understand how the formula method, ratio and proportion, and dimensional analysis organize the same medication relationship, when each method is useful, and why correct setups should agree.
Methodology
Rounding Medication Calculations Safely
Learn nursing dosage-calculation rounding rules, nearest tenth/hundredth language, why verified inputs and intermediate values stay unrounded, and how medication notation differs from device precision.
Methodology
Medication Administration Rights & Safety Checks
Use six core medication administration rights plus broader indication, response, barcode and high-risk safeguards, including when to stop for prescriber clarification or pharmacy formulation advice.
Methodology
How to Check a Medication Calculation Answer
Use one six-step medication-maths check: identify the target, verify active values, align units, assess scale, match supplied limits, then reverse-check the arithmetic.
Methodology
Safe Dose Ranges and Maximum Doses Explained
Calculate lower and upper weight-based limits, keep per-dose and per-day values separate, apply a matching-basis maximum, and compare a prescribed dose without treating arithmetic as clinical approval.
IV & Infusions
6Drip rates, pump rates, infusion maths and fluid balance.
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IV & Infusions
6Drip rates, pump rates, infusion maths and fluid balance.
Formula explainer
IV drip rates explained: drop factor, gtt/min and common errors
Understand what the drop factor means, why gtt/mL and gtt/min are different, how gravity flow relates to mL/hr, and where calculation errors happen.
Calculation guide
mcg/kg/min Infusions Explained: Dose Rate and Pump Rate
Learn how mcg/kg/min connects dosing weight, time and infusion concentration to mL/hr, including forward and reverse calculations, unit checks and high-risk infusion safety boundaries.
Calculation guide
Adding Up Total Fluid Intake and Output
How to combine recorded fluid volumes into one intake total and one output total, with unit matching, decimal alignment and the mistakes that change the result.
Calculation guide
How to Calculate Fluid Balance
Fluid balance is one subtraction: total intake minus total output. This Guide covers the order, the meaning of the sign, how to check the answer, and where the arithmetic stops.
Calculation guide
IV Volume, Time and Rate Explained
Understand how IV volume, time and mL/hr fit together, why the same formula can solve for rate, volume or time, and how to handle minutes, remaining volume and common unit mistakes.
Calculation guide
Medication Dose Rate vs Pump Rate Explained
Understand dose rate versus pump rate, calculate mg/hr from concentration and mL/hr, convert mg/hr and mg/min, and recalculate mL/hr after an authorised medication-rate or concentration change.
Paediatrics
3Maintenance fluids and paediatric calculation methods.
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Paediatrics
3Maintenance fluids and paediatric calculation methods.
Formula comparison
Pediatric maintenance fluids explained: 4-2-1 vs 100-50-20
100-50-20 is the Holliday-Segar daily maintenance method; 4-2-1 is a rounded hourly shortcut based on the same weight bands. This guide explains the relationship, why the totals can differ, and the clinical limits of full maintenance.
Formula explainer
The 100-50-20 Rule for Pediatric Maintenance Fluids Explained
Understand what the 100-50-20 rule estimates, why the first, second and later kilograms use different daily amounts, where the Holliday-Segar method came from, and what the result does not tell you by itself.
Formula explainer
The 4-2-1 Rule for Pediatric Maintenance Fluids Explained
Understand why the 4-2-1 rule uses 4, 2 and 1 mL/kg/hr, how it relates to the daily Holliday-Segar method, how the stepped bands work, and why rounded hourly totals can differ from 100-50-20.
Renal Function
2Cockcroft-Gault, eGFR and renal-estimate selection.
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Renal Function
2Cockcroft-Gault, eGFR and renal-estimate selection.
Formula explainer
The Cockcroft-Gault equation explained
What the Cockcroft-Gault equation calculates, why weight-method selection matters, and when CrCl differs from eGFR.
Formula explainer
eGFR vs CrCl: which renal function estimate should you use?
Understand how CKD-EPI eGFR and Cockcroft-Gault CrCl differ, why their values may not match, and how to follow the estimate and units required by the current source.
Laboratory Calculations
4Anion gap, sodium, calcium and serum osmolality.
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Laboratory Calculations
4Anion gap, sodium, calcium and serum osmolality.
Formula explainer
How to interpret the anion gap
Interpret the anion gap after calculation: local reference interval, albumin, GOLDMARK, DKA limitations, normal-gap acidosis and low or negative gaps.
Formula explainer
Corrected sodium in hyperglycaemia: what the number means
Why high glucose can lower measured sodium, what a corrected sodium estimate represents, why Katz and Hillier differ, and what the number cannot tell you on its own.
Formula comparison
Corrected calcium vs ionised calcium: what's the difference?
A plain-English comparison of total, albumin-corrected and ionised calcium, including why the results can disagree and where correction equations are limited.
Formula explainer
Calculated Serum Osmolality and Osmol Gap Explained
Understand directly measured vs calculated serum osmolality, effective osmolality/tonicity, what the osmol gap represents, why formulas and ethanol coefficients change the result, and why the gap must be interpreted as a clue rather than a diagnosis.
Body Measures & Dosing Weight
3BSA formulas, BSA dosing, ideal and adjusted body weight.
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Body Measures & Dosing Weight
3BSA formulas, BSA dosing, ideal and adjusted body weight.
Formula comparison
Which BSA formula should you use?
A plain-English comparison of Mosteller, Du Bois, Haycock and Gehan & George, why their estimates differ, and how to handle formula choice safely.
Formula comparison
Ideal vs adjusted body weight for medication dosing
Understand the difference between ideal and adjusted body weight, why different dosing weights exist, and why the authorised medicine source must choose the method.
Calculation guide
BSA Medication Dosing Explained: mg/m² to the Patient Dose
Understand what an mg/m² medication order means, how BSA turns it into a patient-specific dose in mg, and why volume, rounding and protocol limits are separate steps.
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