Unit Converter — Length, Weight, Temperature & More

This converter uses the exact, officially-defined relationships between units — not rounded approximations. Every category except temperature shares a single SI base unit, and conversions route through it in two steps so there is never any chained rounding:

1. To the base unit: base = value × factor[from], where factor is the exact number of base units in one of your unit.
2. From the base unit: result = base ÷ factor[to].

The base units are metre (length), kilogram (mass), square metre (area), litre (volume), metre per second (speed), second (time) and bit (digital storage). The factors come straight from the BIPM SI Brochure and NIST Special Publication 811: 1 inch = 25.4 mm exactly, 1 pound = 0.45359237 kg exactly, 1 US gallon = 3.785411784 L exactly, and so on. Because each factor is an exact decimal rational, a round-trip conversion (A → B → A) returns to your original value within floating-point precision — roughly 15 significant digits.

Temperature is different. It is an affine scale, not a simple multiple, so it is handled with explicit formulas through Kelvin rather than a factor table: °F = °C × 9/5 + 32, K = °C + 273.15. The tool also enforces absolute zero (−273.15°C / 0 K / −459.67°F) as a floor and rejects anything colder.

Sri Lankan land units sit in the Area category. Following the Survey Department standard, 1 perch = 272.25 ft² = 25.29285264 m², 1 rood = 40 perches, and 1 acre = 160 perches = 4,046.8564224 m². For digital storage the tool keeps the SI decimal prefixes (1 kB = 1,000 bytes) separate from the IEC binary prefixes (1 KiB = 1,024 bytes), so you can see exactly why a “500 GB” drive shows up as about 465 GiB in your operating system. Every headline conversion is also cross-checked against an independently-published factor, and the result panel shows whether the two methods agree.

• BIPM — The International System of Units (SI Brochure), 9th edition
• NIST Special Publication 811 — Guide for the Use of the SI (exact conversion factors)
• Survey Department of Sri Lanka — land-area equivalences (perch, rood, acre)
• IEC 80000-13 — binary prefixes (kibibyte, mebibyte) vs SI decimal prefixes

Conversion factors on this page were last cross-checked against the sources above on 2026-06-07. SI and NIST definitions are exact and change only when a standards body revises them, which is rare.