Free Online Calculators & Developer Tools

Weight is measured in different units depending on where you live, what you are doing, and which system you grew up with. Most of the world uses kilograms and grams (the metric system), the United States and a handful of other countries rely on pounds and ounces (the imperial system), and the United Kingdom still […]

You have probably heard the advice “drink eight glasses of water a day.” It is one of those rules that gets repeated so often that people assume it is backed by rigorous science. In reality, no single study ever proved that eight glasses is the universal magic number. How much water your body actually needs […]

Volume measures how much three-dimensional space a substance occupies — litres, gallons, millilitres, cups, fluid ounces, cubic metres, and dozens of other units that vary by country, industry, and context. The problem is that these units rarely line up neatly across borders. A recipe from Europe calls for “2 litres of stock” but your measuring […]

A UUID—Universally Unique Identifier—is a 128-bit value usually shown as 36 characters with hyphens, like 550e8400-e29b-41d4-a716-446655440000. The idea is that it’s practically unique across systems and time. You can generate one on your machine without checking a database or asking a central server. So UUIDs get used for primary keys in databases, request IDs in […]

Recipes say grams. Your scale shows ounces. The DIY video uses feet; your tape is in centimetres. Sooner or later you need to convert, and doing it in your head or on a scrap of paper is where mistakes happen. One wrong decimal and your cake is a brick or your cut is too short. […]

A Unix timestamp is the number of seconds since 1 January 1970, 00:00:00 UTC. Logs, APIs, and databases use it because it’s a single number—easy to store, sort, and compare—and it’s the same everywhere until you convert it to a local timezone for display. When you see something like `1735689600` in a log or API […]

How many hours between 9:00 a.m. and 5:30 p.m.? How long from now until your flight? If you add 2 hours 15 minutes to 10:00 a.m., what time do you get? These questions come up all the time—work hours, travel, projects, events—and doing them in your head is where mistakes happen. Cross midnight, and it […]

Temperature is one of those things that’s still split by region. Most of the world uses Celsius. The US (and a few others) uses Fahrenheit. Scientists use Kelvin. So you’re reading a recipe that says “bake at 180 °C” and your oven is in °F. Or the weather app shows 22 °C and you want […]

Tax season has a way of making people nervous. Either they’re afraid they’ll owe more than they saved, or they’re hoping for a refund and don’t want to be wrong. The only way to stop guessing is to have a rough idea of your tax well before the deadline. You don’t need to be an […]

Ever notice that sometimes you wake up after six hours and feel fine, and other times you sleep eight hours and still feel groggy? A lot of that has to do with *when* you wake up—not just how long you slept. Sleep runs in cycles. You go from light sleep to deep sleep to REM […]

A basic calculator does add, subtract, multiply, and divide. A scientific calculator does that plus a lot more: powers and roots, logarithms (log and ln), trigonometry (sin, cos, tan), and often constants like π and e. If you’re in school or university, doing maths or science, or working in engineering or tech, you’ve probably needed […]

Percentages show up everywhere. A sale is 30% off. Your salary went up 10%. You want to leave a 15% tip. Your exam score is 78%. Once you get the hang of it, the maths isn’t hard—but when you’re in a hurry or the numbers are messy, it’s easy to second-guess yourself. A percentage calculator […]