Length Converter

Tool Overview

This tool converts a length or distance from one unit to others. You enter a number and choose the unit it is in. The tool shows the same length in many other units at once. Units are grouped by system: Metric (kilometers, meters, centimeters, millimeters, micrometers, nanometers), Imperial (miles, yards, feet, inches), Nautical (nautical miles, fathoms), and Astronomical (astronomical units, light years). You can search or filter by name or symbol and mark units as favorites so they appear first. So you get the units you use most and can find any unit quickly.

People use different length units in different places. Roads use miles or kilometers. Construction uses feet and inches or meters. Science uses nanometers or astronomical units. Converting by hand is easy to get wrong. This tool does the math for you. It uses meters as the middle step: your input is converted to meters, then from that to each other unit. So every result is consistent.

The tool is for students, builders, travelers, and anyone who works with length or distance. You do not need technical skills. You enter a value, pick the unit, and read the results. An optional search lets you type a phrase (for example 5 miles to km); a remote service may parse it and set the value and unit for you. The conversion itself does not depend on that.

Background & Concept Explanation

Length is how long or far something is. We measure it with units like the meter, the foot, or the mile. Each unit has a fixed relationship to the others. One meter is 100 centimeters. One mile is about 1609 meters. So converting means finding how much of another unit equals the same length. The tool converts your input to meters first, then from meters to each output unit. So there is one internal value and every result is consistent. A related operation involves converting text case as part of a similar workflow.

The tool groups units into four systems. Metric units are based on the meter: kilometers, meters, centimeters, millimeters, micrometers, nanometers. Imperial units are used in some countries: miles, yards, feet, inches. Nautical units are used at sea and in the air: nautical miles and fathoms. Astronomical units are used for very large distances: astronomical units (Earth–Sun distance) and light years. You cannot convert length to a different kind of quantity; you only convert between length units. So you pick a length unit as input and see all other length units as output.

People struggle when they convert by hand. They use the wrong factor. They mix up miles and kilometers or forget how many feet are in a mile. This tool applies the correct factor for each unit. You can search by unit name or symbol to narrow the list. You can star units as favorites so they appear in a Favorites group at the top. So you can work faster with the units you use most.

Key Features

• You enter a length as a number in a text field. The field accepts digits, a decimal point, an optional minus sign, and the characters e and + for scientific notation (for example 1e6). Other characters are removed as you type. The value used for conversion is clamped between a very small and a very large limit (minus 10 to the power 20 to 10 to the power 20). So the input stays valid and the tool does not overflow.
• You choose the unit of your input from a dropdown. The options include all units: km, m, cm, mm, micrometers, nanometers, mi, yd, ft, in, nautical miles, fathoms, astronomical units, and light years. The result list updates when you change the value or the unit. So you see all conversions at once.
• A search field lets you type text to filter the result list. The tool shows only units whose name, symbol, or system contains your search text (case insensitive). So you can type meter or mile or cm to see only matching units. If you type a phrase like 5 miles to km you can click the AI button to ask a remote service to parse it; if the service returns a value and a unit the tool sets the input and unit to that and clears the search. The search query is limited to 200 characters. So you can filter by name or try a natural language phrase.
• Results are grouped. Favorites appear first (units you have starred). Then groups by system: Metric, Imperial, Nautical, Astronomical. The source unit is not shown in the result list (you already have it). Each group header can be clicked to collapse or expand that group. So you can hide groups you do not need and focus on one system.
• Two tabs at the top switch the view. All Units shows all groups (Favorites plus each system). Favorites shows only the Favorites group. So you can see everything or only your starred units.
• Each result row shows a star button, the converted value, the unit symbol, and the unit name. Clicking the star adds or removes that unit from favorites. Favorites are saved in your browser so they persist. A copy button copies the numeric value to the clipboard (not the unit symbol). Very small or very large values are shown in exponential form. So you can copy the number and use it elsewhere.
• Below the input a line shows which unit you are converting from (the full name, for example Meters). So you can confirm the source unit.
• If no units match the search or if you are on Favorites and have no favorites yet, the tool shows a short message. So you know when the list is empty and why.

Common Use Cases

You have a distance in miles and want it in kilometers and feet. You enter the number, choose miles as the source unit, and read the result list. You can search for km or ft to see only those, or scroll to the Metric and Imperial groups. You can copy the value you need. For adjacent tasks, converting currencies addresses a complementary step.

You are working in metric and need to convert meters to centimeters and millimeters. You enter the value, choose meters, and read the Metric group. You can star cm and mm so they appear in Favorites next time.

You have a measurement in feet and inches and want meters. You enter the value in feet (or convert inches to feet first elsewhere), choose feet as the source unit, and read the meters value in the Imperial or Metric section. You can copy the number.

You want to try a phrase like 5 miles to km. You type it in the search field and click the AI button. If the remote service parses it and returns 5 and miles (or km), the tool sets the input to 5 and the source unit to the parsed unit. You then see the result list. If the service fails you can enter 5 and choose miles yourself. So you can use natural language when it works. When working with related formats, converting epoch values can be a useful part of the process.

You use only a few units often. You star them so they appear in Favorites. You switch to the Favorites tab to see only those units. So you get a short list that fits your workflow.

How to Use This Tool

1. Open the length converter in your browser.
2. Type a length in the input field. Use a number with an optional decimal point, minus sign, or scientific notation (e.g. 1e6). The value used for conversion is clamped to a very large range. Choose the unit of your number from the dropdown next to the field (e.g. m, km, mi, ft). The result list updates at once.
3. Optionally type in the search field to filter the list. Only units whose name, symbol, or system match your text are shown. Clear the search to see all units again. The search is limited to 200 characters.
4. Optionally type a phrase like 5 miles to km in the search field and click the AI button (or press Enter). If the remote service parses it and returns a value and a unit that exists in the tool, the input and source unit are set to that and the search field is cleared. If parsing fails you see a short error; enter the value and unit manually.
5. Choose the All Units or Favorites tab. All Units shows Favorites (if any) and then groups by system: Metric, Imperial, Nautical, Astronomical. Favorites shows only starred units. Click a group header to collapse or expand that group.
6. Read each result row: value, unit symbol, and unit name. Click the star to add or remove that unit from favorites. Click the copy button to copy the numeric value to the clipboard. Use the source line below the input to confirm which unit you are converting from.
7. If no units match your search, or you are on Favorites and have no favorites, the tool shows a message. Adjust the search or star some units to see results.

Calculations & Logic

The tool converts every input to meters first. Each unit has a factor (toBase): how many meters one unit of that unit is. For example one kilometer is 1000 meters, so the factor for km is 1000. One foot is 0.3048 meters. One nautical mile is 1852 meters. One light year is about 9.46e15 meters. So to get meters from your input you multiply: base meters = input value × source unit factor. Then to get each output unit you divide: result = base meters ÷ output unit factor. So every conversion goes through meters.

The input value is parsed as a number. If it is not a valid number the tool uses 0. If it is below the minimum limit (minus 10 to the power 20) or above the maximum (10 to the power 20) the tool clamps it to that range. So the value used for conversion is always in a safe range. When the result is very small or very large it is shown in exponential form. When the result is not finite the tool shows Overflow. In some workflows, converting to lowercase is a relevant follow-up operation.

The result list excludes the source unit (you do not see a row for the unit you typed). Results are filtered by the search query: a unit is shown only if its name, symbol, or system (Metric, Imperial, Nautical, Astronomical) contains the search text, case insensitive. If the search field is empty all units except the source are shown. Favorites are stored in the browser; the default favorites are km, m, mi, ft, and in. So the list you see depends on the source unit, the search text, and your favorites.

Reference Tables or Scales

Base unit for conversion is the meter. Each unit has a factor to meters (toBase). Result = (input × source toBase) ÷ target toBase.

Limits: For related processing needs, converting to uppercase handles a complementary task.

Copy copies only the numeric value to the clipboard, not the value plus unit symbol.

Tips, Limitations & Best Practices

Use the search field when you have many units and want one quickly. Type part of the unit name or symbol (e.g. mile, cm, nautical). Clear the search to see all units again. Use Favorites for the units you use most so they appear at the top in the Favorites group.

Enter only a number with an optional decimal point, minus sign, or scientific notation. The tool strips other characters. Values outside the allowed range are clamped. So very large or very small numbers are still handled but may show in exponential form in the result.

The AI search parses a phrase and sets the input and unit. It can fail or return a unit the tool does not have. If you see unit not recognized or could not parse query, enter the value and choose the unit manually. The phrase is sent to a remote service; the conversion math is done in the tool. So you can always convert without using the AI.

Copy copies only the number. If you need the unit as well, note it from the row (symbol and name are shown). Favorites are stored in your browser; if you clear site data they reset to the default set (km, m, mi, ft, in).

Collapsing a group hides its units but does not remove them. Switch to the Favorites tab to see only starred units. If you have no favorites the Favorites tab shows an empty state and a message to star some units.