The ZapUnits blog
Guides that explain the units, not just the arithmetic — where they came from, where they go wrong, and what to watch for when a number crosses a border.
Lunar Time: Why Clocks Run Faster on the Moon
The United States has told NASA to build a lunar time standard by the end of 2026. The reason is not tidiness: a clock on the Moon genuinely ticks faster than one on Earth, by about 56 microseconds every day.
11 October 2026 · 8 min read
GSM Explained: Fabric and Paper Weight Without the Guesswork
One ounce per square yard is 33.906 GSM, exactly. US paper weights are harder, because every grade is weighed at a different sheet size.
3 October 2026 · 6 min read
Isometric Graph Paper: How to Draw in 3D Without Perspective
Three line families, sixty degrees apart, and no vanishing point. Isometric paper lets you draw something in 3D and still measure it.
3 October 2026 · 6 min read
5 mm, 1 cm or Quarter Inch? Choosing a Graph Paper Grid Size
5 mm is the European school standard, quarter inch is the US one, and they are 27% apart. Here is how to pick without guessing.
2 October 2026 · 6 min read
How to Print Graph Paper at Exactly the Right Size
If ten squares of a 5 mm grid do not measure 50 mm, your printer scaled the page. Here is every setting that causes it.
1 October 2026 · 6 min read
Shoe Size Conversion: US, UK, EU and CM Charts That Make Sense
Measure your foot in centimetres and convert from that. Every national scale is just a different way of counting the same length.
29 September 2026 · 7 min read
Gaj to Square Feet: Indian Land Units Without the Confusion
A gaj is simply a square yard: 9 square feet. The trouble starts with bigha, katha and biswa, which change size from state to state.
22 September 2026 · 7 min read
The 28th CGPM, October 2026: Leap Seconds and a Redefined Second
Every four years the CGPM decides what the world's units mean. In October 2026 the agenda includes the death of the leap second and the clock that will replace caesium.
15 September 2026 · 7 min read
US Gallons vs Imperial Gallons: Why a UK Gallon Is 20% Bigger
A US gallon is 3.785 litres and an imperial gallon is 4.546 litres. That 20% gap changes fuel economy, beer and recipe figures.
7 September 2026 · 5 min read
EC Meters Explained: µS/cm, mS/cm, dS/m and PPM
1 mS/cm = 1000 µS/cm = 1 dS/m. Converting to PPM is where meters disagree, because it depends on a conversion factor, not a unit.
24 August 2026 · 6 min read
U-Value and R-Value: Insulation Units Explained
R-value is resistance to heat flow and U-value is the heat that gets through. US R-13 is RSI 2.29. Here is how the units fit together.
10 August 2026 · 6 min read
DPI vs PPI: How Many Pixels You Need for a Sharp Print
Pixels needed = print size in inches × PPI. A 6 × 4 inch photo at 300 PPI needs 1800 × 1200 pixels. Everything else is detail.
27 July 2026 · 5 min read
Acres, Hectares, Bigha and Guntha: Land Area Units Explained
An acre is 43,560 sq ft and a hectare is 2.471 acres. Regional land units are trickier because the same name can mean different sizes in different places.
13 July 2026 · 7 min read
Ounces vs Fluid Ounces: Weight and Volume Are Not the Same
An ounce is 28.35 grams of weight. A US fluid ounce is 29.57 millilitres of space. They only line up for water, and even then not exactly.
29 June 2026 · 5 min read
Feet and Inches to CM: Converting Height Correctly
Multiply the feet by 12, add the inches, then multiply by 2.54. Here is why 5 ft 11 in is not 5.11 feet, and a full height chart.
15 June 2026 · 5 min read
Lakh and Crore to Million and Billion: The Indian Number System Explained
One million is ten lakh. One billion is a hundred crore. Once you see where the commas go, the two systems line up neatly.
1 June 2026 · 6 min read
Six Unit Conversion Mistakes That Cost Millions
A spacecraft lost, an airliner out of fuel at 41,000 feet, and a hospital dosing error — all traced to a unit that was never written down.
25 May 2026 · 7 min read
The Seven SI Base Units and the 2019 Redefinition
In 2019 the last physical artefact defining a unit was retired. Every SI unit is now defined by a constant of nature.
18 May 2026 · 6 min read
Metric vs Imperial: Why the World Still Uses Both
Only three countries have not officially adopted the metric system — but almost every metric country still buys pints, inches or acres.
11 May 2026 · 6 min read
Running Pace: Min/km, Min/mile and Speed
Pace runs backwards from speed — a lower number is faster. That inversion is why the conversion graph curves.
4 May 2026 · 5 min read
mg/dL to mmol/L: Reading Blood Sugar Anywhere
American meters read mg/dL; most of the world reads mmol/L. Divide by 18 and you have it — but only for glucose.
27 April 2026 · 4 min read
mmHg, kPa and Blood Pressure Units Explained
A blood pressure of 120/80 means the pressure would push a column of mercury 120 millimetres up a tube. Here is what that is in modern units.
20 April 2026 · 5 min read
Newton-Metres to Pound-Feet: Torque Without Guesswork
One newton-metre is 0.7376 pound-feet. Get it backwards on a cylinder head and you will find out expensively.
13 April 2026 · 5 min read
Horsepower to Kilowatts: Three Horsepowers Explained
A 'horsepower' is 735.5 watts in Germany and 745.7 watts in America. That 1.4% gap explains a lot of forum arguments.
6 April 2026 · 5 min read
What Is a Kilowatt-Hour? Reading Your Electricity Bill
A kilowatt is a rate. A kilowatt-hour is an amount. Confusing the two is why electricity bills feel mysterious.
30 March 2026 · 6 min read
Calories, Kilocalories and Kilojoules on Food Labels
The Calorie you count is a thousand times bigger than the calorie in a physics textbook. Here is how the units line up.
23 March 2026 · 5 min read
Square Feet to Square Metres: A Property Buyer's Guide
The factor is 0.0929, not 0.3048 — a mistake that makes a flat look three times bigger than it is.
16 March 2026 · 5 min read
PSI to Bar: Tyre Pressure Without the Guesswork
One bar is 14.5 PSI. Get the conversion wrong at a European air pump and you can be 30% under-inflated.
9 March 2026 · 5 min read
Cups to Millilitres: Why Recipes Go Wrong
There are at least four different cups in circulation, ranging from 200 to 284 millilitres. Baking is where that difference bites.
2 March 2026 · 6 min read
Why Your 1 TB Drive Shows Up as 931 GB
Drive makers count a terabyte as a trillion bytes. Windows counts it in powers of two. Both are right; the labels are the problem.
23 February 2026 · 5 min read
Mbps vs MB/s: Why 100 Mbps Downloads at 12 MB/s
Your internet plan is sold in bits. Your download manager counts bytes. There are eight bits in a byte, and that factor explains everything.
16 February 2026 · 5 min read
MPG vs L/100 km: Why Fuel Economy Numbers Never Line Up
Higher MPG is better; lower L/100 km is better. The two are reciprocals, which is why the same car scores 30 MPG in the US and 36 in the UK.
9 February 2026 · 6 min read
Km to Miles: The 0.62 Rule and the Fibonacci Trick
A kilometre is 0.621371 miles. But there is a far more elegant way to convert — and it involves the Fibonacci sequence.
2 February 2026 · 4 min read
Celsius to Fahrenheit: Formula, Shortcuts and a Chart
Temperature scales have different zero points, so conversion needs an offset as well as a factor. Here is the formula and the shortcut.
26 January 2026 · 6 min read
Kg to Lbs: Converting Kilograms to Pounds in Your Head
A kilogram is 2.20462 pounds. Double it and add ten percent — you will land within a quarter of a percent every time.
19 January 2026 · 5 min read
CM to Inches: The Complete Conversion Guide
One inch is exactly 2.54 centimetres — a defined value, not a measurement. Here is how to use it, and the trick for doing it in your head.
12 January 2026 · 5 min read