Historical length converter

Why convert historical lengths?

Before the metric system became widespread, lengths were expressed with many different units. Feet, inches, lines, toises, perches, leagues and cubits can appear in old texts, plans, maps, inventories, deeds, cadastral records and architectural descriptions. Converting these measures to meters or centimeters makes it much easier to understand their approximate size today.

The difficulty is that the same unit name did not always represent exactly the same length. A foot, perch or league could vary by country, region, period or usage. This converter should therefore be used as a comparison and interpretation tool rather than as a universal table valid for every historical source.

Which historical values does the tool use?

To provide consistent conversions, AppErgo uses several reference values. For the French Ancien Régime measures included in the tool, the pied du roi is set to 0.32484 m. The French royal inch is one twelfth of that foot, the line is one twelfth of an inch, the Paris toise is 6 feet, the Paris perch is 18 feet and the Paris league is 2,000 toises.

The converter also includes several ancient reference measures, including the Roman foot, Roman cubit, Roman pace, Roman mile and Egyptian royal cubit. Here too, the displayed values are practical reference equivalents. Historical and archaeological studies may use slightly different values depending on the context.

Modern meter, centimeter and kilometer units are included as well, so a historical measure can be converted directly to a modern reference, or vice versa.

How should the result be interpreted?

The result shows the equivalent calculated from the reference value used by the tool. It is useful for understanding a dimension, comparing measurement systems or testing an interpretation, but it is not a metrological or historical certification. When a source provides the exact value of the unit it uses, that source-specific information should take priority.

The swap button quickly exchanges the source and target measures. The same measure cannot be selected on both sides because converting a unit into itself would provide no useful information.

Why add a personal measure?

This feature exists precisely because historical measurements were not always uniform. If a book, map, archive or study states, for example, that a particular local perch equals 5.72 m, you can create a measure with the name of your choice and define “1 local perch = 5.72 meters”. It then becomes available in the converter lists just like the built-in units.

You can create several personal reference measures and use them in either direction: convert your own measure to meters or another historical unit, or convert a known unit into your personal measure. Each personal measure can be deleted when it is no longer needed.

Local storage, export and import

Personal measures are saved in your browser’s local storage. They therefore remain available on future visits in the same browser, without an account and without sending those values to the AppErgo server. As with any local browser storage, they may disappear if you clear site data, use certain private browsing modes, switch browsers or move to another device.

The “Export” button downloads a backup of your personal measures in an AppErgo file. You can keep this file as a backup or move it to another device. The “Import” button restores measures from such a file. During import, you can either merge the imported measures with those already stored in the browser or replace the current list entirely.

This combination of local storage and import/export lets you keep reference measures tailored to your own research while keeping the tool fully browser-based.