A collection of everyday calculation tools that run entirely in your browser. Convert between metric and imperial units, calculate the number of days between two dates, convert file sizes between bytes and gigabytes, work out percentages, and convert Unix timestamps to readable dates. All with instant results, processed locally in your browser.
Every calculation happens locally in JavaScript. No account is needed and no data is collected. Just open the tool and start calculating.
A calculator is one of the smallest things a computer does. Converting 5 kilometres to miles is a single multiplication. Counting days between two dates is a subtraction with calendar awareness. There is no engineering reason to send the numbers to a server, wait for a response, and pay the latency cost. The browser can do it in microseconds.
The inputs are also things that simply do not need to be uploaded for the math to work. A date subtraction, a percentage, a unit conversion all run in a few lines of JavaScript. There is no good reason for those few lines to live on a remote server.
In-browser calculators show the result as you type. All processing happens locally in your browser. Close the page and there is no trace.
How the calculators work
Each calculator is a small JavaScript function. The unit converter has a lookup table of SI and imperial conversion factors and applies the relevant multiplication. The date calculator uses the browser's built-in Dateobject, with the millisecond-since-epoch representation under the hood. The percentage calculator does the three classic percentage operations (X percent of Y, X is what percent of Y, percentage change between two values). The byte converter handles both decimal (SI) and binary (IEC) units side by side.
All math runs in JavaScript's 64-bit floating-point, which gives about 15 significant digits of precision. That is more than enough for any unit conversion or percentage you would do without a spreadsheet.
In-browser calculators vs the alternatives
Approach
Speed
Effort
Best for
In-browser (this site)
Instant
Open page, type
One-off lookups, ad-hoc questions
Search engine quick conversions
Fast (after a round trip)
Type query
Quick conversions when search is already open
Spreadsheet applications
Setup time
Build formula
Repeated calculations on many rows
For a single conversion or a quick date calculation, a dedicated in-browser tool is faster than typing into a search bar and waiting for the answer card. For repeated calculations on many values, a spreadsheet is the right answer.
When to use these tools
Working with everyday measurements? Switch metric and imperial values with the unit converter, or work out file sizes between bytes and gigabytes using the byte converter.
Splitting a restaurant bill with friends? The tip and split calculator handles gratuity per person, and the discount calculator finds the sale price after a percent-off promotion.
Doing percentage math for a school assignment or budget? The percentage calculator covers the three common operations (X percent of Y, what percent X is of Y, and change between two values).
Marking a milestone? Work out your exact age in years, months, and days with the age calculator.
Frequently asked questions
Are these calculator tools free?
Yes. No usage limits, no account, no ads.
Do these calculators need an internet connection?
Only for the first page load. After that, every calculation runs locally in JavaScript. You can disconnect from Wi-Fi and the calculators keep working.
How accurate are the unit conversions?
The conversion factors come from official SI and NIST definitions. Internally everything is computed in double-precision floating-point, which is accurate to about 15 significant digits. For everyday conversions the result is exact to as many digits as you would normally care about.
Why is the date calculator giving a result that looks one day off?
Almost always a timezone issue. Dates entered without a time default to midnight in the browser's local timezone. If you cross daylight saving time during the calculated range, the count of days between two midnight values can differ from a wall-clock estimate by one. The result is correct in calendar days.
Does the byte converter use 1024 or 1000 as the base?
Both. The tool shows decimal (SI) units alongside binary (IEC) units. A megabyte (MB) is 1,000,000 bytes by SI; a mebibyte (MiB) is 1,048,576 bytes by IEC. Different contexts use different conventions, so the tool shows both.
Is the Unix timestamp converter aware of leap seconds?
No, because Unix time itself does not count leap seconds. The tool follows the standard POSIX convention used by every operating system and programming language: each day has exactly 86400 seconds.
Why is there no calculation history?
Keeping a history would mean writing your inputs to local storage. Since the appeal of these tools is that nothing is stored, we deliberately keep no history. Copy the result to a note app if you need to keep it.