無料オンライン単位変換ツール – 単位と測定値を変換

Open the site and use the top 'Category' dropdown to pick 'Length', enter your number in the left input labeled 'Value (from)', choose 'meter (m)' from the left 'From unit' dropdown and 'foot (ft)' on the right 'To unit' dropdown, then click the 'Convert' button (or press Enter). The page shows the converted value with up to 9 decimal places by default and a small 'Copy' button to put the result on your clipboard. Use the 'Swap' button to quickly reverse units; inputs accept scientific notation like 1e6 and restrict values roughly between 1e-9 and 1e12 to avoid JavaScript precision loss.

Yes — select 'Weight' under 'Category', pick 'kilogram (kg)' and 'pound (lb)', or click 'Upload CSV' to batch-convert. The CSV uploader accepts .csv files up to 5 MB and up to about 50,000 rows comfortably in desktop Chrome/Firefox; it asks you to map the input column to the 'Value' field and choose the output unit, then use the 'Convert All' button and 'Download CSV' to save results (output file is .csv with a header). On mobile Safari large uploads can fail due to limited JS heap; if you need larger batches, split files or run conversions in Excel or a script for reliability.

Choose 'Temperature' in the 'Category' dropdown, type your temperature into 'Value (from)'—the input accepts negatives and decimals such as -17.5—and pick '°C' and '°F' in the unit selectors, then press 'Convert'. The converter uses the exact formula F = C × 9/5 + 32 and returns a result shown to 4 decimal places by default; you can change precision under 'Settings' to 0–12 decimals. Extremely small fractional inputs (e.g., 1e-8) render correctly but may show floating-point artifacts above 12 digits; use the 'Reset' button to clear fields or re-enter values if a pasted string contains commas which trigger an 'Invalid number' error.

The tool includes a broad metric-to-imperial set: length units (mm, cm, m, km, inch, foot, yard, mile), mass/weight (mg, g, kg, ounce, pound, stone), volume (mL, L, US fl oz, US pint, US gallon, UK fl oz, UK pint, UK gallon), speed (m/s, km/h, mph, knots), area (cm², m², ha, acre, ft²), and time (s, min, h, day, week, month, year). Abbreviations like 'm', 'kg', 'ft' are shown in dropdowns and results; the converter does not currently include esoteric units like 'smoot' or specialized survey feet variants. For ambiguous units (US vs Imperial gallon) the unit selector labels the system (US/UK) so you can pick the intended conversion.

The 'Currency' category pulls rates from a public FX feed and displays the timestamp next to the 'Update rates' button so you can confirm freshness; rates refresh automatically approximately once per hour and you can force a manual update. The site supports over 170 currencies (EUR, USD, GBP, JPY, etc.) and allows single conversions or CSV exports (.csv) of converted columns; cached rates are used when offline or when the fetch fails, with a note that cached data is up to 24 hours old. There are no hidden fees or signups — conversions are free — but small rounding differences compared to bank rates may appear because the tool uses mid-market rates, not live bank margins.

The site is tested on the latest Chrome, Firefox and Edge on desktop and Chrome/Firefox on Android; it also works on Safari desktop and iOS Safari, but iOS Safari has a smaller JavaScript heap so large CSV uploads or very large batch operations (>20 MB or >50k rows) may fail. Clipboard actions (Copy button) require HTTPS and user gesture permissions, and the numeric keypad is shown automatically on mobile when input fields are focused. For best stability with big datasets use desktop Chrome or Firefox; for quick single conversions the mobile UI is fully functional and includes the same 'Convert', 'Swap' and 'Download CSV' controls.

Open 'Settings' (gear icon) and choose either 'Decimal places' from 0–12 or switch to 'Significant figures' mode where you can set 1–12 significant digits; the default is 4 decimal places. Behind the scenes the tool uses JavaScript Number (IEEE 754) so you get up to ~15–17 significant digits of reliable precision; extremely large integers above ~1e15 may lose integer precision, which is a known JS limitation. For scientific-grade precision beyond that, export your CSV and use a bignum-aware desktop tool or Python with the decimal module; the tool displays a warning when input exceeds the safe integer threshold.

Select 'Volume' from 'Category', set 'Value (from)' to the liters column or paste values separated by newlines into the multi-input box, choose 'liter (L)' and 'US gallon (gal)' or 'UK gallon (gal, imperial)' and press 'Convert'. Use 'Download CSV' to export results as a .csv file with a header row; desktop browsers handle exports up to about 10,000 converted rows reliably before memory slows or triggers the page to hang. If you need larger datasets, convert in chunks or export multiple CSVs; the exporter respects your chosen decimal/precision setting from 'Settings'.

Pick 'Speed' in the 'Category' dropdown, enter your value(s) (single or multiple newline-separated speeds), choose 'kilometer per hour (km/h)' as From and 'mile per hour (mph)' as To, then press 'Convert'; the tool uses exact conversion factors such as 1 mph = 1.609344 km/h. It also supports 'knot' and 'm/s' and displays unit labels in results; you can paste GPS-derived CSVs and map a column to the speed field during upload. When working with timestamped telemetry, export the converted column (.csv) and open in Excel for plotting — browser-based conversion is convenient but not a substitute for GIS/time-series tools for advanced analysis.

The 'Time' category converts durations between units such as milliseconds, seconds, minutes, hours, days, weeks, months and years; select your input and output units and click 'Convert' or paste multiple duration values line-by-line into the multi-input box. Months are treated as 30 days and years as 365 days for straightforward arithmetic, so the converter does not account for calendar-specific details like leap years, leap seconds or time zones — it is a pure duration converter, not a datetime-aware tool. For timezone-aware or calendar-accurate conversions, export the durations (.csv) and use a datetime-capable application or scripting library.

A frequent error is 'Invalid number' caused by thousands separators like '5,000' or pasted text with non-numeric characters; remove commas or paste plain digits or use scientific notation (1e3). CSV upload problems often stem from wrong delimiter — use 'Upload settings' to switch between comma, semicolon or tab delimiters before mapping columns. If the currency rate fetch fails you’ll see 'Rate fetch failed' with a timestamp and a retry button; retry or use cached rates (displayed with age). Large-batch memory errors on mobile typically mean splitting the CSV or switching to desktop Chrome/Firefox will resolve the issue.

Unit Converter Online Free is optimized for quick interactive conversions, single-value work and small-to-medium CSV batches with direct download as .csv, whereas Excel or a scripting language provides stronger automation, macros and better handling of millions of rows with native 64-bit precision. Desktop apps are preferable for very large datasets, advanced rounding rules, or when you need to embed conversions into workflows; the online tool’s advantage is zero-install, instant UI controls ('Category', 'From unit', 'To unit', 'Convert', 'Download CSV') and no signup. Pro tip: do bulk conversions in the site to validate unit logic, then export the converted CSV and open it in Excel for further filtering, pivot tables or charting.