Free Online Calculators & Converters
Accurate, fast, and beautifully simple tools for everyday calculations — built by an engineer who uses them daily.
Why Calculating.app?
Most calculator sites are cluttered with ads, slow to load, and give you a number with zero context. We built Calculating.app to be different.
Speed first
Server-side rendered pages load instantly. No waiting for JavaScript to show you the answer. Every page targets under 2.5 seconds Largest Contentful Paint.
Answers with context
A calculator result is more useful when you see the formula, step-by-step breakdown, nearby values, and related conversions. We show you the full picture, not just a number.
Verified accuracy
All formulas follow international standards — SI units, ISO 8601 for dates, NIST reference values for temperature. Sources are documented and reviewed.
Multilingual
Every calculator is available in English and Russian, with proper localization — not machine translation. Content is adapted for how people actually search in each language.
Calculator Categories
Explore our growing collection of free online tools
Date Calculators
Add or subtract days from any date, calculate your exact age, count days between two dates, seasonal countdowns, and more. Live countdowns and rich date context for every result.
Includes: Days from today, Age calculator, Days between dates, Time since, Days till summer/winter/spring/autumn, Korean age
Temperature Converters
Convert between Fahrenheit, Celsius, and Kelvin with full formula breakdowns and step-by-step arithmetic. Includes all six conversion directions — and we're one of the few sites covering Kelvin conversions.
Includes: Fahrenheit to Celsius, Celsius to Fahrenheit, Kelvin to Celsius, Celsius to Kelvin, Kelvin to Fahrenheit, Fahrenheit to Kelvin
Length Converters
Convert inches, feet, centimeters, millimeters, and meters. Supports combined inputs like '5 feet 10 inches' for natural height queries. Proximity tables show nearby values at a glance.
Includes: Inches to mm, Inches to cm, Inches to meters, Inches to feet, Feet to inches, Feet to meters, Feet to cm, Feet to mm
Number Tools
Convert numbers to Roman numerals, binary, and back. Every result page shows the complete step-by-step conversion process — not just the answer, but how we got there.
Includes: Number to Roman numerals, Roman to number, Decimal to binary, Binary to decimal
More Tools
QR code generator, IP address lookup, Chinese zodiac animal of the year, and more utilities coming soon.
Includes:
Built by an Engineer
About the author
I'm Roman Naumenko, a software engineer with over a decade of experience building web applications. I created Calculating.app because I was tired of reaching for the same everyday calculators — days between dates, temperature conversions, unit lookups — and finding only slow, ad-heavy pages that gave a bare number with no context. This project is my answer: fast, accurate tools with full formula explanations, built on modern server-side rendering technology for instant results. Every formula is verified against international standards before publication.
Our Approach to Accuracy
Every calculator on this site follows a strict quality standard. Formulas are sourced from international standards (SI, ISO 8601, NIST). Each calculation shows the complete step-by-step derivation so you can verify the result yourself. Date calculators reference ISO 8601 and handle edge cases like leap years and timezone boundaries. Temperature conversions use exact NIST conversion formulas. Length conversions use precise SI-defined factors.
Frequently Asked Questions
Are these calculators free to use?
Yes, all calculators on Calculating.app are completely free. No registration, no subscriptions, no hidden fees.
How accurate are the calculations?
All calculations use verified formulas from international standards — SI units, ISO 8601 for dates, and NIST reference values. Each result page shows the formula and step-by-step breakdown so you can verify the math yourself.
What languages are supported?
Currently English and Russian. All content is natively written, not machine-translated, to ensure natural phrasing and correct terminology in each language.
Can I use these calculators on my phone?
Yes. The site is fully responsive and optimized for mobile devices. Pages are server-rendered for fast loading even on slower connections.
Who built this site?
Calculating.app is built and maintained by Roman Naumenko, a software engineer with a degree in mathematics and 20 years of experience in software development.
Questions, suggestions, or found an error?
Get in touch