Unit Converter

This tool is a general-purpose unit converter implemented as a single PHP page: unit-converter/index.php.

It accepts a numeric input value, a unit category (distance, mass, volume, temperature, area, speed, time, pressure, energy, power, data, angle), and a source unit. When you submit the form the tool converts the value into every supported unit in the chosen category and displays a tidy results table.

Goals / design

• Simple, self-contained PHP UI that works without JavaScript (JS enhances UX but is not required).
• Each category has a stable base unit. Conversions go: input unit -> base -> output unit. Temperature uses explicit formulae because it's not a pure multiplier.
• Output precision is configurable.

Location

• Tool code: unit-converter/index.php
• Documentation: unit-converter/unit-converter.md

How to use (UI)

1. Open unit-converter/index.php in your web server (for example, http://localhost/proishs-webtools/unit-converter/).
2. Select a category from the Category drop-down.
3. Enter a numeric value and pick the From unit for that value.
4. (Optional) Change Precision — number of decimal places in the table output.
5. Click Convert.

The page will display a table converting your input to all supported units in the chosen category.

Programmatic API

The page uses POST form parameters. You can also call it with GET for convenience.

Parameters:

• category — category key (distance, mass, volume, temperature, area, speed, time, pressure, energy, power, data, angle).
• value — numeric value to convert.
• from — unit code (see the supported units table below).
• precision — integer number of decimal places (0–12).

Example (GET):

/unit-converter/index.php?category=distance&value=1&from=km&precision=4

This will show conversion of 1 kilometer into every supported distance unit.

Supported categories and units

The tool attempts to cover common SI and imperial units. Each entry shows the unit code used in the UI.

• distance (base: meter m)

  • mm Millimeter
  • cm Centimeter
  • m Meter
  • km Kilometer
  • in Inch
  • ft Foot
  • yd Yard
  • mi Mile

• mass (base: kilogram kg)

  • mg Milligram
  • g Gram
  • kg Kilogram
  • t Metric ton
  • oz Ounce
  • lb Pound

• volume (base: liter l)

  • ml Milliliter
  • l Liter
  • m3 Cubic meter
  • tsp Teaspoon (US)
  • tbsp Tablespoon (US)
  • cup Cup (US)
  • floz Fluid ounce (US)
  • pt Pint (US)
  • qt Quart (US)
  • gal Gallon (US)

• temperature (base: Kelvin K) — special handling

  • C Celsius
  • F Fahrenheit
  • K Kelvin
  • R Rankine

• area (base: square meter m2)

  • mm2 Square millimeter
  • cm2 Square centimeter
  • m2 Square meter
  • km2 Square kilometer
  • in2 Square inch
  • ft2 Square foot
  • acre Acre
  • ha Hectare

• speed (base: m/s)

  • m/s Meters per second
  • km/h Kilometers per hour
  • mph Miles per hour
  • knot Knot
  • ft/s Feet per second

• time (base: second s)

  • ms Millisecond
  • s Second
  • min Minute
  • h Hour
  • day Day

• pressure (base: Pascal Pa)

  • Pa Pascal
  • kPa Kilopascal
  • bar Bar
  • atm Atmosphere
  • psi Pound per square inch

• energy (base: Joule J)

  • J Joule
  • kJ Kilojoule
  • cal Calorie
  • kcal Kilocalorie
  • Wh Watt hour
  • kWh Kilowatt hour

• power (base: Watt W)

  • W Watt
  • kW Kilowatt
  • MW Megawatt
  • hp Horsepower

• data (base: Byte B)

  • B Byte
  • KB Kilobyte (1000)
  • KiB Kibibyte (1024)
  • MB Megabyte (1000^2)
  • MiB Mebibyte (1024^2)
  • GB Gigabyte (1000^3)
  • GiB Gibibyte (1024^3)
  • TB Terabyte

• angle (base: radian rad)

  • deg Degree
  • rad Radian
  • grad Grad

Implementation notes

• The conversion table for non-temperature categories uses multiplicative factors relative to a base unit. Example: inches -> meters uses factor 0.0254.
• Temperature conversions use helper functions to convert to Kelvin and back because they require offsets and scaling.
• Precision is clamped to a reasonable range (0–12) in the UI.

Extending the tool

To add a category or a new unit:

1. Open unit-converter/index.php.
2. Update the units_definitions() array: add a category key, define base and units with code=>['name'=>..., 'factor'=>...]. For temperature-like categories add special handlers.
3. Save and reload the page.

Notes on adding temperature-like categories: any unit that requires more than a linear multiplier needs its own pair of conversion functions (to/from base). Follow the temp_to_kelvin() and kelvin_to_temp() pattern.

Examples

• Convert 5 kilometers to all distance units: choose category distance, value 5, from km.
• Convert 32 Fahrenheit to Celsius & Kelvin: category temperature, value 32, from F.

Tests

Minimal test checklist:

• UI test: select each category and convert a sample value (1 or 100) to ensure the page returns a table with no errors.
• Sanity checks for well-known conversions:
  • distance: 1 km -> 1000 m
  • mass: 1 lb -> 0.45359237 kg
  • temperature: 0 C -> 273.15 K and 32 F -> 0 C
  • data: 1 KiB -> 1024 B
• Edge cases:
  • Very large numbers (1e12) and very small numbers (1e-12) — check precision formatting.
  • Invalid category or unit — the UI falls back to a safe default (distance).

Caveats and limitations

• The tool is intentionally simple and synchronous. For very large data sets or many batched conversions, consider implementing an API endpoint that streams results or a background job.
• Unit lists are not exhaustive. Add or tweak factors in units_definitions() as needed.

Next improvements (suggested)

• Add copy-to-clipboard buttons beside each result.
• Support selecting a subset of target units to show.
• Add CSV/JSON export of results.
• Add automated unit tests (PHPUnit) to verify conversion factors.

Contact / contribution

Contributions are welcome — open a pull request with unit additions or fixes. When adding units, include a brief source for conversion factors (official SI tables or authoritative references).