Unit conversion guide: SI, temperature and digital storage

Convert only compatible quantities

A unit conversion changes the numerical value and unit while preserving the physical quantity. Length converts to length and mass converts to mass; kilograms cannot be converted to metres without an additional relationship such as density and geometry. Select the measurement category before choosing source and target units.

Linear units use a scale factor through a common base unit. Temperature scales also use offsets, so converting 0°C is not done by multiplying one factor. The calculator applies the appropriate Celsius, Fahrenheit and kelvin relationships separately from length, weight and storage factors.

Distinguish decimal and binary prefixes

SI prefixes use powers of ten: kilo means 1,000 and mega means 1,000,000. BIPM guidance says SI prefixes should not represent powers of two. Digital systems also use binary prefixes: kibi is 1,024 and mebi is 1,048,576. Confusing MB with MiB produces a visible difference in storage reports.

The current BIPM SI brochure includes expanded prefixes and current conventions; its 2025 revision updated parts of the reference material, including binary-prefix information. SableApps labels decimal kilobyte and binary kibibyte separately so the selected factor is explicit.

Preserve appropriate precision

A calculator can display many digits, but the source measurement may support only a few. Converting 1.2 metres to 120 centimetres does not make the measurement more precise. Retain suitable significant figures and include uncertainty when the result supports scientific, engineering or regulated work.

Exact defined conversion factors differ from approximate measured relationships. The inch is exactly 0.0254 metre, but a physical measurement in inches still has instrument uncertainty. Do not round intermediate calculations repeatedly; convert with full precision and round the reported value once.

Use current authoritative definitions

Since 2019 the SI base units have been defined through fixed numerical values of fundamental constants. This strengthens global consistency without changing ordinary conversion arithmetic. The BIPM maintains the SI brochure and reference material, so consult the current edition when symbols, prefixes or high-precision definitions matter.

For trade, medicine, construction and laboratory reporting, local regulation can control accepted units, calibration and rounding. A browser converter is suitable for everyday estimates and cross-checks, not a calibration certificate. Record the source unit explicitly and never infer it only from a bare number.

Worked example: storage and physical measurements

A drive maker's 500 GB label uses decimal gigabytes, while an operating system may display a binary-based capacity or use inconsistent wording. Convert 500 gigabytes to gibibytes to explain the numerical difference without claiming storage disappeared. Keep bytes, bits and transfer rates separate; eight bits make a byte, but protocol overhead can still reduce observed throughput.

For a 6-foot room dimension, convert feet to metres and retain precision appropriate to the original measurement. If the tape reading was only precise to a fraction of an inch, reporting many decimal places in metres would be false precision. For temperature, verify source scale before entry: 32°F converts to 0°C, while treating 32 as Celsius produces an entirely different physical condition.

Write units so others can reproduce the conversion

Unit symbols are case-sensitive: m means metre, while M is the SI prefix mega. Leave a space between a number and an SI unit symbol in formal writing, and do not pluralize symbols. Store the original value, original unit, conversion factor or method and rounded result when a calculation feeds engineering, pricing or reporting.

Area and volume factors must be squared or cubed. One metre equals 100 centimetres, but one square metre equals 10,000 square centimetres. The current simple converter covers linear length, mass, temperature and storage; it intentionally avoids guessing area, volume, speed or compound-unit relationships that need their own dimensional rules.

Quick checklist

• Choose the correct physical quantity.
• Keep source and target units visible.
• Distinguish kB from KiB and MB from MiB.
• Use offset-aware temperature conversion.
• Match rounding to source precision.
• Consult authoritative rules for regulated measurements.

Primary references

Standards and platform support change. Use these authoritative sources to check the current specification and migration guidance.

• BIPM — Current SI brochure
• BIPM — The International System of Units