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Measurement Units
Keep a unit beside every number, especially when an estimate changes from area to volume or from volume to mass.
Choose a unit for the quantity being entered
Length, area, volume and mass are separate kinds of quantity. A depth is a length; a floor is an area; a material layer has a volume. Do not put a square-unit value into a length field because the same material is involved.
The calculation model supports defined metric and customary units. The selectors shown for a particular field are limited to the kind of quantity that field accepts.
Read the available unit families
Use the label displayed beside the field or result.
| Quantity | Examples of defined units |
|---|---|
| Length | m, cm, mm, in, ft, yd |
| Area | m², ft², yd² |
| Volume | m³, L, ft³, yd³, US gallon, imperial gallon |
| Mass | kg, lb, metric tonne, US short ton |
A unit change should preserve the measurement
The conversion model uses exact definitions where available, including 1 inch = 0.0254 m and 1 foot = 0.3048 m. Area and volume factors are derived from the corresponding squared or cubed length factors.
Changing the display unit describes the same stored quantity. A short display value should not be repeatedly written back as a new measurement. If you deliberately edit the number after switching units, that is a new input and should be reviewed as such.
Coverage and density need both parts of the unit
Paint coverage combines area and volume, such as m²/L or ft² per explicitly identified gallon. Density combines mass and volume, such as kg/m³ or lb/ft³. Enter the unit that belongs to your product information.
US and imperial gallons are distinct definitions. Likewise, metric tonnes and US short tons are not interchangeable. An imported unqualified ton value needs a choice or a volume-only treatment; it should not be guessed.
Keep meaning when exporting or importing
Project records and structured exports retain stable unit identifiers and calculation inputs. Readable labels may be formatted for the page, but the machine values must not change meaning with wording.
When checking a CSV, compare each quantity with its unit column. A number copied into a spreadsheet without its unit can be ambiguous even if the number itself is correct. When an import reports an unsupported or ambiguous unit, resolve that field before accepting the project.
Frequently asked questions
Why are weight and volume not interchangeable units?
They describe different quantities. Converting between them needs an applicable density, not just a unit conversion factor.
Sources and method
- NIST — SI Units ↗
Reference for length, mass, area, volume and the distinction between base and derived units.
- NIST Guide to the SI — Conversion Factors ↗
Reference for unit conversions and clear identification of metric and customary units. Exact base-unit definitions are retained in calculations rather than rounded display factors.
- PackLedge product documentation
Instructions for the calculators, browser-local projects, user prices and downloadable project records.