Length Converter

The page opens on the Length converter and the category dropdown lists 29 entries. Twenty-four are factor-based measurement categories carrying 200 unit definitions: length (12), area (10), weight (11), volume (14), temperature (5), time (12), digital storage (11), parts per (6), speed (7), pace (4), pressure (10), current (6), voltage (7), power (9), reactive power (5), apparent power (5), energy (13), reactive energy (4), flow rate (9), illuminance (7), frequency (8), angle (7), torque (7) and electric charge (11). Four more are format converters rather than unit converters: number to English words, words to number, number to Roman numerals and Roman numerals to number. Currency is listed but disabled, because live rates would need a network call the rest of the tool never makes.

Most converters answer a single from/to question and make you re-run the tool for the next pair. The All Results tab flips that. Pick the source unit, type a value, and the page renders every unit in the category at once as a grid of cards, each showing the unit name, symbol, formatted result and its own copy button. The source unit's card is highlighted so you can see where the chain started. Enter 1 in length and you get 12 answers; volume gives 14, energy 13, electric charge 11. It is the fastest way to sanity-check an order of magnitude before a number lands in a spec sheet or a BOM. The six custom-formula categories are excluded and say so.

General converters stop at length, weight and temperature, which is why engineers keep three tabs open. This one carries the categories that actually block hardware and firmware work, on the same page as bytes and ppm, so a power calculation and a storage calculation do not need two different sites. Real, reactive and apparent power sit in three separate categories rather than one blurred list, and electric charge is deep enough to settle a battery question in mAh without a second tool. Every factor ships compiled into the page, so nothing shifts between visits and nothing depends on an API staying up.

Silent rounding is how conversion tools lose trust. Here the formatter picks precision from the magnitude of the result: below 0.0001 it prints 10 decimal places, below 1 it prints 8, below 100 it prints 6 and below 10,000 it prints 4, always stripping trailing zeros so 2.5000 reads as 2.5. Larger values are grouped with en-US thousands separators and capped at two fraction digits. Once a magnitude reaches 1e15, or drops below 1e-10 without being zero, output switches to exponential notation with six decimals, the only sane rendering for electronvolts, statamperes or light years. The underlying arithmetic is standard IEEE-754 double precision; formatting changes display only, and the copy button copies exactly what is on screen.

The conversion path is arithmetic in your tab: multiply by the source factor to reach the base unit, divide by the target factor. There is no fetch, no XHR and no localStorage in that path, no account to create and no file to upload, so pasting a pressure rating from an unreleased product or a battery capacity from a client spec carries no disclosure risk. Copy uses the clipboard API with an execCommand fallback; download builds the .txt receipt from a Blob and an object URL, entirely locally. Because all 200 factors ship with the page instead of being fetched, the converter returns identical answers on every visit and keeps working when the connection does not.

The dropdown lists 29 entries: 24 factor-based measurement categories holding 200 unit definitions, four number-format converters, and Currency, which is disabled. The largest categories are volume (14 units), energy (13), length (12), time (12), weight (11), digital storage (11), electric charge (11), area (10) and pressure (10). The smallest are pace (4) and reactive energy (4). Every unit carries a name, a symbol and one explicit factor to its category base unit: meter, kilogram, liter, second, byte, pascal, watt, joule, coulomb, lux, hertz, degree or newton-meter.

No. Each conversion is two operations in the browser tab: the input times the source unit's factor to reach the base unit, then divided by the target unit's factor. There is no fetch, no XHR, no localStorage and no upload anywhere in the conversion path, so nothing you type leaves the page. Currency is the proof. It is the one category that would need live exchange rates over the network, and it returns an error rather than opening a connection. No account, no signup, no file upload.

Length uses the meter as base with exact international definitions: 1 mile = 1609.344 m, 1 yard = 0.9144 m, 1 foot = 0.3048 m, 1 inch = 0.0254 m and 1 nautical mile = 1852 m. Metric prefixes are exact powers of ten, from kilometer at 1000 down to nanometer at 1e-9, and one light year is 9.461e15 m. Neighbouring categories follow the same discipline: 1 acre = 4046.8564224 m², 1 US gallon = 3.785411784 L, 1 UK gallon = 4.54609 L, 1 pound = 0.45359237 kg.

Binary throughout. Byte is the base unit: 1 bit = 0.125 B, 1 KB = 1024 B, 1 MB = 1,048,576 B, 1 GB = 1,073,741,824 B, 1 TB = 1,099,511,627,776 B and 1 PB = 1,125,899,906,842,624 B. Four IEC units are listed separately, kibibyte through tebibyte, and they map to the same powers of 1024, so KB and KiB return identical numbers here. There is no pebibyte entry. If you need decimal drive-vendor sizing where 1 GB = 1,000,000,000 B, this converter will not produce it.

Temperature is the one factor-free category: five scales converted through explicit formulas with Celsius as the pivot. Incoming, Fahrenheit is (F − 32) × 5/9, Kelvin is K − 273.15, Rankine is (R − 491.67) × 5/9 and Réaumur is Ré × 5/4. Outgoing, Celsius becomes C × 9/5 + 32 for Fahrenheit, C + 273.15 for Kelvin, (C + 273.15) × 9/5 for Rankine and C × 4/5 for Réaumur. Because these are affine rather than multiplicative, temperature is flagged as a custom converter and left out of the All Results grid.

Number to Roman numerals accepts 1 through 3,999,999 and returns the error Number out of range (1-3999999) outside it. Above 3,999 it uses vinculum (overline) forms, where an overlined M is 1,000,000, D is 500,000, C is 100,000, L is 50,000, X is 10,000 and V is 5,000, with subtractive pairs at 900,000, 400,000, 90,000, 40,000, 9,000 and 4,000. Standard subtractive notation applies below 1,000: CM, CD, XC, XL, IX, IV. The reverse converter uppercases input, tests two-character vinculum sequences before single letters, and rejects any unrecognised character.

Number to Words converts the integer part only, using ones and teens up to nineteen, tens words through ninety, and scale words for thousand, million, billion, trillion, quadrillion and quintillion. Tens are hyphenated (twenty-three), hundreds insert and before the remainder (one hundred and five), and negatives are prefixed with negative. The reverse direction lowercases the input, strips and plus punctuation, accepts either negative or minus as the sign, multiplies by 100 on hundred, and accumulates each scale group. Note the asymmetry: the reverse map stops at quadrillion, so quintillion parses only in the forward direction.

Precision is chosen by magnitude, not a fixed decimal count. Values under 0.0001 are rendered to 10 decimal places, under 1 to 8, under 100 to 6 and under 10,000 to 4, with trailing zeros stripped so 2.5000 reads as 2.5. Anything larger is grouped with en-US thousands separators and capped at two fraction digits. Magnitudes at or above 1e15, and non-zero magnitudes below 1e-10, switch to exponential notation with six decimals, which is what keeps electronvolts (1 eV = 1.602176634e-19 J) and light years readable.

Yes, through the All Results tab. Choose the source unit first, then type the value: the tool converts it into every unit of the active category at once, rendering one card per unit with the unit name, symbol, formatted result and a copy button, and highlighting the source unit's card. Length returns 12 cards, volume 14, energy 13 and electric charge 11. The six categories flagged as custom converters, meaning temperature, the four number-format converters and currency, are excluded and show a notice instead.

Electrical coverage runs deeper than most general converters: current (6 units, including abampere and statampere), voltage (7, including abvolt and statvolt at 299.792458 V), power (9, with metric horsepower at 735.49875 W and imperial at 745.699872 W), reactive power in var, mvar, kvar, Mvar and Gvar, apparent power in VA, mVA, kVA, MVA and GVA, reactive energy in varh, kvarh, Mvarh and Gvarh, energy (13 units, 1 kWh = 3,600,000 J, 1 BTU = 1055.06 J) and electric charge (11 units, 1 Ah = 3600 C, 1 mAh = 3.6 C, 1 faraday = 96,485.33212 C).

No. The Currency entry appears in the dropdown but every attempt returns Currency conversion requires live exchange rates. Coming soon! instead of a number, and the category holds zero unit definitions. Rates move by the second, so they cannot be embedded as static factors, and fetching them would mean a network request that breaks the guarantee that nothing leaves the page. Every other converter uses fixed physical or definitional factors that never go stale, so they behave identically offline and return the same answer on every visit.

Two ways, both local. Copy writes the formatted result with navigator.clipboard.writeText when the page is in a secure context, and falls back to an off-screen textarea plus document.execCommand('copy') when it is not. Download assembles a short plain-text receipt, listing category, input with source symbol and output with target symbol, as a Blob, hands it to an object URL and saves it as category-conversion-timestamp.txt. The per-card copy buttons in the All Results and All Converters grids call the clipboard API directly, without the textarea fallback.