What Is Ohm's Law? V = I × R Explained Simply
Ohm's law links voltage, current, and resistance with one equation: V = I × R. Learn the triangle trick and see worked examples.
Lena Hoffmann · 4 min read
Guides & tutorials
Practical guides, how-tos and comparisons to get the most out of our free online tools.
December 31, 2025
December 30, 2025
The One-Mile Walk Test, and What a VO2max Estimate Assumes
The Rockport test turns a brisk one-mile walk into a VO2max number using five inputs and one published regression. Here is the equation, one person worked through it, and the two assumptions — a stated standard error and a genuinely brisk pace — that decide whether the answer means anything.
Sofia Nunes · 14 min read
The Right Rice-to-Water Ratio for Every Type of Rice
Learn the exact water ratio for white, brown, basmati and jasmine rice using the absorption method — no measuring guesswork.
Marco Bianchi · 4 min read
December 29, 2025
Relative Risk and Absolute Risk Are Not the Same Story
A headline saying 50% higher risk can describe a change of two-tenths of a percentage point. Both numbers come from the same 2x2 table, and computing both takes one line each — here is how, with a worked example, number needed to treat, and where the odds ratio stops approximating relative risk.
Sofia Nunes · 12 min read
How to Set a Freelance Hourly Rate That Actually Pays You
Set a freelance rate from your target salary, real billable hours and business costs — so you don't undercharge by treating a rate like a salaried wage.
Camille Laurent · 4 min read
December 26, 2025
Corrected Calcium: Why Albumin Changes the Number
About half of blood calcium is bound to albumin and inactive, so a total-calcium result on a low-albumin patient reads low even when the active fraction is normal. Here is the correction in both unit systems, a worked case, and the honest verdict on how badly it performs.
Sofia Nunes · 13 min read
What Is Customer Churn Rate? Formula and How to Reduce It
Customer churn rate measures how fast you lose customers. Learn the formula, why it caps growth and shortens lifetime value, and how to reduce it.
Daniel Okonkwo · 4 min read
December 25, 2025
Blood Sugar Units: mg/dL, mmol/L, and Why Both Exist
The conversion factor is not 18 — it is 18.016, and it is the molar mass of glucose divided by ten. Here is where it comes from, which countries use which unit, and every diagnostic threshold in both scales with the guideline it belongs to.
Sofia Nunes · 13 min read
Growth Percentiles: What a Child's Centile Really Means
A centile ranks a child against a reference population — it is not a grade, and one reading says almost nothing. Here is the LMS arithmetic behind the number, and why the same boy is on the 90th centile on one chart and the 85th on another.
Sofia Nunes · 14 min read
December 24, 2025
What a Standard Drink Actually Is
A standard drink is a defined mass of ethanol — and the definition changes at the border. The same glass of wine is 1.28 drinks in the United States, 1.79 in France and 2.28 in the United Kingdom.
Sofia Nunes · 12 min read
How to Multiply and Divide Fractions: Multiply Across, Flip to Divide
Multiplying fractions needs no common denominator — just multiply across. Dividing means multiplying by the reciprocal. Learn both with worked examples and how to simplify.
Lena Hoffmann · 3 min read
December 23, 2025
Net Carbs: What the Subtraction Assumes
Net carbs is total carbohydrate minus fibre minus sugar alcohols. Every term in that line is a modelling choice, the first one is defined differently on each side of the Atlantic, and no regulator anywhere defines the result.
Sofia Nunes · 12 min read