MedMaths Calculation Guides
Browse plain-English Guides by the clinical problem you are trying to solve. Each Guide connects the calculation to its formula, worked method, limitations, safety boundaries and supporting references.
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Medication Calculations
Dose, tablet, weight-based and medication-unit calculations explained step by step.
Explore GuidesMedication Preparation
Read labels, measure volumes, reconstitute medicines and separate reconstitution from dilution.
Explore GuidesMedication Safety & Foundations
Build the habits around units, rounding, reasonableness, dose limits and safe administration.
Explore GuidesIV & Infusions
Understand gravity drip rates, volume-time-rate relationships, pump rates and weight-based infusions.
Explore GuidesPaediatrics
Compare paediatric maintenance-fluid methods and understand the daily and hourly rules.
Explore GuidesRenal Function
Understand Cockcroft-Gault, eGFR and why the renal estimate required by a source matters.
Explore GuidesLaboratory Calculations
Interpret anion gap, sodium correction, calcium correction and serum osmolality calculations.
Explore GuidesBody Measures & Dosing Weight
Compare BSA formulas, BSA medication dosing and ideal versus adjusted body weight.
Explore GuidesFeatured Guides
A few useful places to start
These examples show the range of MedMaths Guides: reading medication information, understanding an IV calculation, and comparing paediatric fluid methods.
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
Paediatric 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.
Full directory
All MedMaths Guides
Every Guide is listed below by clinical area. Use the quick-jump links to move through the library.
Medication Calculations
3Dose, tablet, weight-based and medication-unit calculations explained step by step.
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
5Read labels, measure volumes, reconstitute medicines and separate reconstitution from 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 recognising 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.
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
7Build the habits around units, 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 organise 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
4Understand gravity drip rates, volume-time-rate relationships, pump rates and weight-based infusions.
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
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
3Compare paediatric maintenance-fluid methods and understand the daily and hourly rules.
Formula comparison
Paediatric 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 Paediatric 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 Paediatric 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
2Understand Cockcroft-Gault, eGFR and why the renal estimate required by a source matters.
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
4Interpret anion gap, sodium correction, calcium correction and serum osmolality calculations.
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
3Compare BSA formulas, BSA medication dosing and ideal versus 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.
Another way to browse
Choose the kind of explanation you need
Clinical area is the main directory. Guide type is a secondary way to understand what each resource is designed to do.
Formula explainers
9Understand what an equation measures, what its inputs mean and where its limitations begin.
Formula explainers
Calculation guides
11Work through units, formulas and worked methods before or after using a calculator.
Calculation guides
Comparisons
5See why similar methods differ and what the current protocol or reference needs you to use.
Formula comparisons
Safety & methodology
6Check how calculations, rounding, administration and verification decisions should be approached.
Methodology
One topic, connected support
Use MedMaths at the depth you need
Calculate
Get the arithmetic now, with the formula and working kept close to the result.
Understand
Use a Guide for context, limitations, comparisons, safety boundaries and worked methods.
Learn and practise
Study one idea at a time, then practise it without losing your place.