Everything Metric: Add-on for Firefox and Chrome

Personal Project; Everything Metric is an extension for Chrome and add-on for Firefox browsers to improve the usability of U.S. websites for international users. The extension/add-on makes an automatic conversion of Imperial and US Customary units to Metric units. For the sake of the good User Experience, conversion is done in-line without any user interaction, and the whole page is "translated" on the page load.

Example: 10 ft are shown as 10 ft (3 m)˜

The page you are reading can also be used for testing the installed extension. With the extension installed and active all bottom units should have Metric conversions shown next to them.

Firefox Add-ons Store: Everything Metric - Firefox Add-on

Chrome Web Store: Everything Metric - Chrome Extension

The U.S. customary system (USC or USCS) of units is similar to the British Imperial System, both derived from English units which had its roots in Roman and Anglo-Saxon units. While the rest of the world transitioned to metric, the U.S., Myanmar, and Liberia are the only countries that didn't transition yet.

The U.S. government passed the Metric Conversion Act of 1975, which made the metric system "the preferred system of weights and measures for U.S. trade and commerce", but it has been left up to the industry to voluntarily convert to Metric System. The scientist in the U.S. already use Metric units, but consumers can rarely see metric units in their daily lives outside Nutritional Facts food labels.

Length

For measuring length, the USCS uses the inch, foot, yard, and mile.

To demonstrate how complicated it is, a length of 1 metre can be seen written in many ways in USCS:

39.37 inch

39.37 in

39.37″

39-6/16″

39 3/8″

39-3/8″

39 ⅜″

39⅜″

3.28 ft

3.28 feet

3.28′

3′ 3.37″

3 ft 3.37 in

3′-3 3⁄8″

3′ 3 3⁄8″

3′ 3-3/8″

3′ 3⅜″

3′-3⅜″ (fractions as 1 Unicode character)

3′-3 ⅜″

1.09 yards

1yd 3.37in

1yd 0.28ft

There are many other "creative" ways to write foot, inch and their symbols.

Per ISO 31-1 the symbol for the inch is "in" which is also denoted with a double prime symbol ″

but people also write these capital letters ("In", "IN"), full words ("Inch) with or without first letter in uppercase, and use improper variations of double prime symbol as quotes (”), double apostrophes (’’), twice typed prime character (′′), and other ways. One inch can be seen written as

1"

1″

1”

1’’ - two apostrophes

1′′ - twice typed prime character

1'' - twice typed single quote character

1in

1 in

1 In

1 IN

1 inch

1 Inch

Half an inch can be seen written as

1/2″

½″ - fraction as a single Unicode character

1⁄2″ - fraction as 3 characters

0.5″

.5″

plus all other variations of the symbol ″ listed above.

Per ISO 31-1 the symbol for the foot is "ft" which is also denoted with prime symbol ′

One foot can be seen written as

1'

1’

1′

1ft

1 ft

1 foot

One and a half inch can be seen written in various ways with various different ways the spaces, dashes and other symbols are used. These are some of the ways this can be seen in various websites:

1 1/2"

1 1/2″

1 1/2”

1 1/2’’

1 1/2′′

1 1/2''

1 1/2in

1 1/2 in

1 1/2 inch

1 1/2 inches

1-1/2"

1-1/2″

1-1/2”

1-1/2’’

1-1/2′′

1-1/2''

1-1/2in

1-1/2 in

1-1/2 inch

1-1/2 inches

1 1/2"

1.5"

1 1⁄2"

1 ½"

1½"

1.5″

1 1⁄2″

1 ½″

1½″

1.5”

1 1⁄2”

1 ½”

1½”

The measurements above several inches are written as a combination of feet and inches, and can be seen written in many different ways:

2′4″

2'4"

2’4’’

2’4”

2′ 4″

2' 4"

2’ 4’’

2’ 4”

2′−4″

2'−4"

2’−4’’

2’−4”

2 ft 4 in

2ft 4in

2ft-4in

2 foot 4 inches

This creates an issue because the same symbols internationally represent time: 2′ 4″ is 2 minutes and 4 seconds.

Volume in USCS

There are fluid and dry volume units in USCS, and for example, a dry gallon is a different volume than a fluid gallon. The extension assumes that the fluid units are used instead of the dry units, as these are more common, although many write fluid ounces as simply oz, and the extension cannot know which ones are meant.

All following measurements denote the same volume:

1 gallons

1 gal

4 quarts

4 qt

8 pint

8 pt

16 cp

16 cups

128 fl oz

128 fl ounces

There are also other USCS units for fluid volume like a barrel, shot, gill, hogshead... which are ignored by the extension as these are less commonly used.

The gallon, quart, pint, cups and the rest are different in the UK, and the extension checks for the website's domain is .UK to switch to Imperial units instead of USCS.

There are also measurements of Teaspoon and Tablespoon, but each country assumes different volume for both, as with the cup.

Cups are different depending on a country: Australia and Canada (250 mL), U.K. (284.13 mL), U.S. (236.59 mL). Even in the U.S., there is a difference in volume between a US tablespoon (14.79 mL) and a US tablespoon used by the FDA (15 mL). The same difference within the U.S. exists also for Teaspoons and Cups. 

Weight in USCS

In the U.S. a pound of feathers weighs more than a pound of gold (453 g / 373 g), but an

ounce of feathers less than an ounce of gold (38 g / 31 g). This is because one is Avoirdupois pound/ounce and the other is US Troy pound/ounce. Troy units are used for precious metals only.

A weight of one pound can be seen written as

1 pound

1 lbs

1 lb

16 ounces

16 oz

USCS also has a "short ton" and a "long ton", dram, bushel, and grain. The extension does not convert those units as they are rarely used. For the "ton" conversion it wouldn't be possible to determine which one it is, as these have different weights, and it would be also possible to confuse it with a metric ton (1000 kg) with the same abbreviation "t".

The extension also converts:

Temperature

32.02 °F

82 °Fahrenheit

Area

600 square feet apartment

600 square foot apartment

600 sq ft

600 sqft

600 ft²

Volume

1 cu ft

100 in³

and other units

80 mph

35 mpg

The extension/add-on is attempting to at simplify the mess in these units. Not all "creative" ways of writing these units are taken into account yet, but I am trying to improved extension in my free time.

Microsoft Edge version of this extension is planned in the near future.

Happy browsing!