UnitLens: Free Online Unit Converter — 15 Categories
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Whether you are a student converting metres to miles for a physics assignment, a chef trying to work out how many grams are in a cup of flour, a developer checking how many gigabytes fit in a terabyte, or a traveller calculating fuel efficiency on a road trip abroad, you need a fast, reliable unit converter that works across every category of measurement without switching between different tools. That is exactly what UnitLens by ExcelGuru was built to deliver.
UnitLens is a free, browser-based online unit converter that covers 15 distinct measurement categories and more than 200 individual units. With its intelligent smart search, live bidirectional conversion, full conversion table, recent history, and one-click Excel export, UnitLens is the most comprehensive free unit conversion tool available without a sign-up or subscription.
In this complete guide, we will walk through every feature of UnitLens, explain how to use it, and detail every unit available across all 15 categories — giving you everything you need to convert any measurement, any time.
What Is UnitLens and Why Is It Different?
A unit converter is a tool that translates a measurement expressed in one unit into its equivalent value in one or more other units. Basic unit converters have existed on the web for decades, but most of them are cluttered with advertising, limited to a single category per page, or require multiple clicks to reach the unit you need. UnitLens was designed from the ground up to solve these frustrations.
The defining features that make UnitLens different are its smart search bar, which lets you type a value and unit in plain language and be taken directly to the right converter with the value pre-filled; its universal all-conversions table, which displays every unit in the active category simultaneously rather than making you select pairs one at a time; and its Excel export, which downloads a complete structured conversion report — a feature no other free unit converter tool offers.
UnitLens is also built as a single self-contained HTML file with all identifiers namespaced under the `uc-` prefix, meaning it can be embedded into any website, blog, or web application without conflicting with existing code. It is fully responsive and optimised for mobile devices, with a slide-in category drawer and touch-optimised controls that make it as easy to use on a phone as on a desktop.
How to Use the UnitLens Smart Search
The smart search bar at the top of UnitLens is the fastest way to reach any converter. It understands natural language input combining a numeric value with a unit name or symbol. Typing “5 miles” automatically opens the Length converter with 5 miles pre-filled as the source value. Typing “100 kg” opens the Weight converter with 100 kilograms pre-filled. Typing “72°F” or “72 fahrenheit” opens the Temperature converter with 72 degrees Fahrenheit ready to convert. Typing “500 GB” opens the Data and Storage converter pre-filled with 500 gigabytes.
The search also recognises unit names without a numeric value. Typing “kilowatt” finds the Power category and takes you directly to the kilowatt unit. Typing “atmosphere” finds the Pressure category. Typing “parsec” finds Length. This makes UnitLens an effective unit discovery tool for anyone who knows what they want to convert but is not sure which category it falls under.
Search results appear in a dropdown beneath the search bar, showing the matched unit name, its symbol, and its parent category. Selecting any result loads the appropriate converter instantly. The search is ranked by match quality — exact symbol matches appear first, followed by prefix matches, followed by partial name matches.
Pro tip: Most unit symbols work directly in the search bar. Try “kPa”, “AU”, “kWh”, “lbf”, “GHz” — UnitLens recognises hundreds of standard unit symbols and abbreviations.
How to Convert Between Units: Step by Step
Using the main converter interface in UnitLens is straightforward. Each category provides two selector dropdowns — “From” and “To” — each containing every unit in that category. You type the value you want to convert into the “From” field, select the source unit, and select the target unit. The result appears instantly in the large green display below, updated in real time as you type.
The swap button between the two selectors reverses the direction of conversion with a single click — if you have just converted 5 miles to kilometres, pressing swap converts the result in kilometres back to miles, making it easy to explore a conversion in both directions without re-entering the value.
The “To” field also accepts manual input. If you type a value into the right-hand field and then change the unit selectors, the displayed result updates accordingly. This bidirectional design means you can work from either end of the conversion — either specifying the source value you have, or specifying the target value you need and working backwards to understand what the source would be.
Below the main converter card, the All Conversions table shows the source value converted into every unit in the active category simultaneously. Every value in this table is clickable to copy to the clipboard. This table is particularly useful when you need to understand relative magnitudes across an entire unit system — for example, seeing 1 kilometre expressed as metres, centimetres, millimetres, miles, yards, feet, inches, and nautical miles all at once.
Simulating Color Blindness with ColorLens
Approximately 8% of males and 0.5% of females have some form of color vision deficiency. This means that for every hundred users who visit your website or application, eight or more may perceive your carefully chosen colors in a significantly different way than you intended. The Color Blindness tab in ColorLens makes this visible.
ColorLens simulates six distinct types of color vision deficiency by applying scientifically validated transformation matrices to each of your palette’s five primary shade stops. The simulations run simultaneously so you can compare them side by side without switching between modes.
Deuteranopia (reduced green sensitivity, affecting approximately 6% of males) causes greens to appear yellowish and makes red-green distinction difficult. Protanopia (reduced red sensitivity) makes reds appear very dark and increases confusion between red and green. Tritanopia (reduced blue sensitivity, extremely rare at approximately 0.01% of people) causes blues to appear greenish and yellows to appear pinkish. Achromatopsia (complete color blindness, affecting approximately 0.003% of people) renders all colors as shades of gray — the most extreme simulation. Deuteranomaly is the most common color vision deficiency overall and reduces green sensitivity without eliminating it entirely.
Reviewing these simulations before finalising a color palette is a professional accessibility practice that prevents one of the most common and easily avoided design failures: relying on color alone to convey meaning.
Complete Guide to All 15 Conversion Categories
UnitLens covers every major category of physical measurement used in everyday life, science, engineering, computing, and commerce. Below is a complete reference to all 15 categories and the units available within each.
Category | Units | Includes |
📏 Length | 16 units | nm, mm, cm, m, km, in, ft, yd, mi, nmi, AU, ly, pc, fur, ftm, µm |
⚖️ Weight / Mass | 13 units | µg, mg, g, kg, t, oz, lb, st, US ton, long ton, carat, grain, troy oz |
🌡️ Temperature | 5 units | °C, °F, K, °R (Rankine), °Ré (Réaumur) |
◻️ Area | 10 units | mm², cm², m², km², ha, ac, mi², yd², ft², in² |
🧪 Volume | 16 units | mL, L, m³, fl oz, cup, tbsp, tsp, pt, qt, gal (US/UK), bbl, cm³, ft³, in³ |
🚀 Speed | 7 units | m/s, km/h, mph, ft/s, knot, Mach, speed of light |
⏱️ Time | 13 units | ns, µs, ms, s, min, h, d, wk, mo, yr, decade, century, millennium |
💾 Data / Storage | 11 units | bit, B, KB, MB, GB, TB, PB, KiB, MiB, GiB, TiB |
⚡ Energy | 11 units | J, kJ, MJ, cal, kcal, Wh, kWh, MWh, BTU, eV, ft·lb |
🌀 Pressure | 9 units | Pa, kPa, MPa, bar, mbar, atm, PSI, mmHg, inHg |
🔋 Power | 9 units | mW, W, kW, MW, GW, hp (mech), PS (metric), BTU/h, ft·lb/min |
📐 Angle | 6 units | °, rad, grad, turn, arcmin (′), arcsec (″) |
⛽ Fuel Economy | 6 units | L/100km, km/L, MPG (US), MPG (UK), km/gal, mi/L |
🏋️ Force | 8 units | N, kN, MN, lbf, kgf, dyne, poundal, ozf |
〰️ Frequency | 8 units | mHz, Hz, kHz, MHz, GHz, RPM, rad/s, cycles/min |
Length Converter
The Length category is UnitLens’s most-used converter and includes 16 units spanning the full range of human-scale and astronomical measurement. For everyday use, the tool converts between the metric system (nanometres, millimetres, centimetres, metres, kilometres) and the imperial system (inches, feet, yards, miles) with full precision. For scientific and navigational contexts, it also includes the nautical mile (used in maritime and aviation navigation), the fathom (used in water depth), the furlong (used in horse racing), and the astronomical unit (the average Earth–Sun distance, used as a baseline in solar system measurements). For deep-space astronomy, UnitLens supports the light-year and the parsec — the two standard units of stellar and galactic distance.
Weight and Mass Converter
The Weight and Mass category covers 13 units across metric, imperial, US, and specialist systems. The core metric units (micrograms, milligrams, grams, kilograms, tonnes) are all present, as are the full imperial range (ounces, pounds, stone, long tons) and the US short ton. For jewellery and gemstones, UnitLens includes the carat (200 milligrams), and for precious metals trading it includes the troy ounce (approximately 31.1 grams), which differs from the standard avoirdupois ounce. The grain, a very small unit historically used for gunpowder and pharmaceutical measurements, is also included.
Temperature Converter
Temperature conversion is one of the most frequently searched unit conversions on the web, driven primarily by Celsius-to-Fahrenheit conversion for cooking and travel. UnitLens supports five temperature scales: Celsius (the metric standard), Fahrenheit (used in the United States for everyday temperature), Kelvin (the SI base unit, used in physics and chemistry, starting at absolute zero), Rankine (an absolute temperature scale used in some engineering applications, particularly in the United States), and Réaumur (a historical scale still occasionally referenced in some European food traditions). All five convert to and from each other correctly, including the non-linear conversions that involve additive offsets rather than simple multiplication.
Data and Storage Converter
The Data and Storage category is particularly valuable for technology professionals and includes both the decimal SI prefixes (kilobyte = 1,000 bytes, megabyte = 1,000,000 bytes) and the binary IEC prefixes (kibibyte = 1,024 bytes, mebibyte = 1,048,576 bytes). The distinction between these two systems is a frequent source of confusion — hard drive manufacturers use decimal prefixes, while operating systems traditionally report storage in binary units, which is why a 1 TB drive appears as approximately 931 GiB in Windows. UnitLens covers bits, bytes, kilobytes, megabytes, gigabytes, terabytes, petabytes, and their binary counterparts (KiB, MiB, GiB, TiB).
Energy Converter
The Energy category serves nutritionists, physicists, and engineers alike. It includes the SI joule and its multiples (kilojoule, megajoule), the calorie and kilocalorie (kcal) used in nutrition labelling, electrical energy units (watt-hour, kilowatt-hour, megawatt-hour) used in power consumption and billing, the British Thermal Unit (BTU) used in heating and cooling specifications, the electronvolt used in particle physics, and the foot-pound used in mechanical engineering. The kilowatt-hour is arguably the most commercially important unit in this category, being the unit in which residential electricity is billed globally.
Fuel Economy Converter
Fuel economy is a category where different regions use fundamentally different measurement approaches, creating genuine confusion for international travellers and car buyers. Europe and most of the world measure fuel economy as litres consumed per 100 kilometres (L/100km) — lower is more efficient. The United States uses miles per gallon (MPG) with US gallons — higher is more efficient. The United Kingdom historically used miles per gallon with Imperial gallons, which are approximately 20% larger than US gallons, making UK MPG figures higher than US MPG figures for the same vehicle. UnitLens also includes km/L (common in Japan and parts of Asia) and miles per litre. Because all these units involve a reciprocal relationship, UnitLens handles the non-linear conversion automatically.
Key Features of UnitLens
Conversion History
Every conversion you perform in UnitLens is automatically added to a Recent Conversions history log displayed at the bottom of the panel. The history stores the last 20 unique conversions with the category icon, the full conversion string (e.g. “5.000 mi = 8.047 km”), the category name, and the time the conversion was performed. Clicking any history entry reloads that exact conversion — category, units, and value — making it easy to revisit or build on previous work without retyping.
Favorites
The Favorite button in the converter toolbar lets you star any category for quick reference. Favorited categories are counted in the live ticker bar at the top of the page. This is useful for people who regularly convert within a specific domain — a chef who frequently converts between volume units, or a developer who regularly converts data storage units, can mark those categories as favorites for faster access.
Excel Export
The Download Table button generates a structured Excel workbook with three sheets. The first sheet contains the full conversion table for the currently active category — every unit converted from the current source value, with unit names, symbols, converted values, unit types, and category labels. The second sheet provides an all-categories summary showing sample conversions from the base unit of each category. The third sheet exports the full conversion history from the current session. This Excel report is designed to be useful in professional contexts: engineers documenting design calculations, teachers preparing reference sheets, scientists recording unit conversions for a lab report, or anyone who needs a permanent record of their conversion work.
Mobile Optimisation
On mobile devices, the 15-category sidebar collapses into a slide-in drawer accessed via the “All Categories” button. The input row stacks vertically for comfortable thumb use. The ticker bar simplifies to show the four most important metrics. All swatches, buttons, and inputs are sized for touch interaction. The tool has been tested on iOS Safari, Android Chrome, and mobile Firefox.
UnitLens vs Other Online Unit Converters
The unit conversion tool market is competitive, with well-established players including UnitConverters.net, ConvertWorld.com, RapidTables.com, and the built-in conversion features of Google Search. UnitLens differentiates from all of these in several important ways.
Smart natural language search is genuinely rare in this category — most converters require you to navigate to the right category page first, then select your units. UnitLens’s ability to parse “5 miles” or “100 kg” and land you directly in the right converter with the value pre-filled saves several clicks on every use. All-conversions table — showing every unit simultaneously rather than just a pair — is a significant time-saver for anyone exploring an unfamiliar unit system. Excel export is unique in the free tier: no comparable free tool offers a downloadable structured conversion report. And zero advertising means the interface is clean and fast, with no distraction or privacy-compromising ad tracking.
Conclusion: The Only Unit Converter You Will Ever Need
UnitLens by ExcelGuru brings together all the unit conversion functionality you will ever need — from the everyday (metres to feet, kilograms to pounds, Celsius to Fahrenheit) to the highly specialised (parsecs to light-years, electronvolts to joules, Rankine to Kelvin, L/100km to MPG) — in a single, fast, free, mobile-ready tool that works in any browser without a sign-up.
Whether you use it for a quick one-off conversion or as a regular companion for professional technical work, UnitLens delivers accuracy, speed, and the uniquely powerful combination of smart search, simultaneous all-unit display, and Excel export that no competing free tool can match.
UnitLens by ExcelGuru is free, requires no sign-up, works offline after first load, and stores no data. Open it on any device and start converting immediately.
Frequently Asked Questions
How accurate are the conversions in UnitLens?
All conversion factors in UnitLens are sourced from the International Bureau of Weights and Measures (BIPM) SI standards and the US National Institute of Standards and Technology (NIST). The tool uses JavaScript’s 64-bit IEEE 754 floating-point arithmetic, which provides approximately 15–16 significant digits of precision — more than sufficient for any practical application. Results are displayed with up to 10 significant figures, and very large or very small results are shown in standard scientific notation.
Does UnitLens work without an internet connection?
Yes. Once the page has loaded in your browser (including the Google Fonts stylesheet), UnitLens operates entirely offline. All conversion logic runs in your browser using JavaScript — no data is sent to any server. You can also save the HTML file to your device and open it locally for fully offline use.
Why are there two different sets of units for data storage (KB vs KiB)?
The difference arises from two incompatible standards. In the decimal (SI) system, a kilobyte is exactly 1,000 bytes — this is used by storage manufacturers, network providers, and the SI standard. In the binary (IEC) system, a kibibyte is 1,024 bytes — this is used by operating systems and many software applications. UnitLens includes both because the confusion between them is a frequent source of real-world discrepancy, and converting between them is a common professional need.
Can I convert fuel economy between L/100km and MPG?
Yes. UnitLens includes a dedicated Fuel Economy category covering L/100km, km/L, MPG (US), MPG (UK), km/gallon (US), and miles/litre. Because fuel economy is a reciprocal relationship (more litres per 100km means worse economy; more miles per gallon means better economy), UnitLens handles the non-linear conversion formula automatically — you simply enter the value and select the target unit.
Is the Excel export compatible with Google Sheets and Mac Numbers?
Yes. The UnitLens Excel export generates a standard .xlsx file compatible with Microsoft Excel, Google Sheets, LibreOffice Calc, and Apple Numbers. The file opens without formatting issues in all these applications.
How does the smart search handle ambiguous unit names?
When a unit name appears in multiple categories (for example, “gallon” appears in both Volume and Fuel Economy), UnitLens returns all matching units in its search dropdown, showing the category name next to each result so you can choose the right one. Results are ranked by match quality, with exact symbol matches appearing before partial name matches.