Historical & Specialized Units Converter
A flexible converter for rare, obsolete, archival and “niche” measurement systems. Choose a category (length, mass, volume, typography, maritime/astronomical), pick a unit and we’ll convert it to a modern reference unit and back to another specialized unit.
Values are best-effort, widely cited references.
Conversion done via the category’s base unit (m, kg, L, mm or m).
Tip: to compare two strange units (e.g. Roman mile → league), choose the same category, set “from” to Roman mile, “to” to league.
How we convert
to_value = from_value × (from_factor_to_base ÷ to_factor_to_base)
Example (Historical length): 1 Roman mile (1479 m) → league (4828.032 m)
value_in_league = 1 × (1479 ÷ 4828.032) ≈ 0.3065 league
Each category has its own base: meters, kilograms, liters, millimeters, or meters again (for maritime/astronomical). We state typical values but museums, navies and national standards may differ.
Reference values used here
| Historical length (base: meter) | |
|---|---|
| Unit | To meter |
| Egyptian royal cubit | 0.5235 m |
| Biblical cubit (~18 in) | 0.4572 m |
| Roman foot | 0.296 m |
| Roman mile | 1479 m |
| League (land) | 4828.032 m |
| Historical & trade mass (base: kilogram) | |
|---|---|
| Unit | To kilogram |
| Stone (UK) | 6.35029318 kg |
| Troy ounce | 0.0311034768 kg |
| Tola (India) | 0.0116638 kg |
| Catty (China) | 0.60478982 kg |
| Scruple (apothecary) | 0.0012959782 kg |
| Historical / trade volume (base: liter) | |
|---|---|
| Unit | To liter |
| US gill | 0.118294118 L |
| UK gill | 0.1420653125 L |
| Oil barrel (US) | 158.9872949 L |
| Hogshead (US wine) | 238.4809424 L |
| US dry bushel | 35.23907017 L |
| Typography & printing (base: mm) | |
|---|---|
| Unit | To mm |
| PostScript point (1/72 in) | 0.352777778 mm |
| PostScript pica (12 pt) | 4.233333333 mm |
| Didot point | 0.375 mm |
| Maritime & astronomical (base: meter) | |
|---|---|
| Unit | To meter |
| Nautical mile | 1852 m |
| Fathom | 1.8288 m |
| Astronomical unit (exact) | 149,597,870,700 m |
About historical units
Before SI and national standards, units were pragmatic: the length of an arm, the capacity of a barrel, the yield of a field. That means: the same name, different places, different values. We picked commonly cited modern reference approximations (museums, NIST tables, well-known engineering handbooks).
How to use this tool safely
- Always note the source (city, period) if you are doing academic work.
- For maritime or aviation use, rely on current national/ICAO/IMO definitions.
- For book & type history, double check with the printing specification of the era.
FAQ
1. Can I convert, say, a tola to a hogshead?
They’re different dimensions (mass vs volume), so the tool won’t mix those. Pick a category where units share a base dimension.
2. Why isn’t my local historical unit here?
There are hundreds. We included a solid core to cover many research and hobby cases. You can simulate yours by using a nearby unit and scaling the input value.
3. Do you support SI directly?
Yes — in each category there’s a modern “base” unit (meter, kg, liter, mm). Convert historical → base → export to another system.