Metric and Imperial Conversion Tables and Formulas

Author: Ian C. Langtree - Writer/Editor for Disabled World (DW)
Published: 20 Dec 2017 - Updated: 4 Jul 2026
Publication Type: Conversion, Calculation

Table of Contents:
Synopsis - Definition - Introduction - Main - Insights, Updates - Related Content

Synopsis: This information sets out formulas and conversion factors for translating between metric and imperial units across length, area, volume, weight, and temperature, giving a full picture of how measurements relate between the two systems. It works through common conversions such as inches to centimeters, gallons to liters, and Celsius to Fahrenheit, alongside less obvious distinctions like the gap between U.S. and British gallons and fluid ounces. Because the tables lay out multiplication factors rather than requiring a calculator app or internet connection, they are especially practical for seniors, people with disabilities, or anyone who prefers working measurements out by hand.

At a Glance

• 1 - The metric system was first fully described by English scholar John Wilkins in 1668, roughly 120 years before France officially adopted it.
• 2 - A hard conversion rounds a measurement to a more convenient number, while a soft conversion keeps the original figure exact without altering it.
• 3 - Although Americans commonly spell the units meter and liter, metre and litre remain the official spellings recognized by the International Bureau of Weights and Measures.

Topic Definition: Measurement Conversion

Measurement conversion is the process of expressing a quantity, such as length, weight, volume, or temperature, in a different unit or system of measurement while preserving its actual value. It relies on fixed mathematical relationships, called conversion factors, that describe how one unit compares to another, such as how many centimeters make up an inch or how many liters make up a gallon. Conversion becomes especially important when moving between the metric system, used by most of the world, and the imperial or U.S. customary system, still common in the United States for everyday measurements.

Introduction

Metric System

The metric system is a decimalised system of measurement in the sense that all multiples and sub-multiples of the base units are factors of powers of ten of the unit. Fractions of a decimal unit are rarely used.

The metric system, and metre was first fully described by Englishman John Wilkins in 1668 in a treatise presented to the Royal Society some 120 years before the French adopted the system. It is believed that the system was transmitted to France from England via the likes of Benjamin Franklin. In the U.S. Americans frequently spell 'metre' as 'meter', and 'litre' as 'liter'; however 'metre' and 'litre' are the official BIPM names for these units.

Main Content

Imperial System

Imperial units are the measurement units that were historically used in the British Commonwealth countries. They were very similar, but not identical, to the units that are still predominantly used in the United States. Some of the differences are:

• 1 U.S. fluid ounce = 1.041 British fluid ounces
• 1 British fluid ounce = 0.961 U.S. fluid ounce
• 1 U.S. gallon = 0.833 British Imperial gallon
• 1 British Imperial gallon = 1.201 U.S. gallons

Our handy conversion tables below show you the formulas to convert from metric system measurements to the imperial system and visa versa allowing you to do your own calculations for the conversion you need. Measurement conversions include weight, mass, length, volume, and temperature.

Hard and Soft Measurement Conversions

Hard Conversions

A hard conversion (adaptive conversion) may not be exactly equivalent. A hard conversion changes the measurement to numbers and units in the new system that are easier to work with. Nominal values are sometimes allowed and used, and a hard conversion sometimes involves a slightly different substitution configuration, or measurement, of the item in question.

Soft Conversions

Some conversion measurements from a system of units to another needs to be exact - this means there is no increasing - or decreasing - the precision of the first measurement unit. This is called soft conversion. Soft conversion does not involve changing the actual physical configuration of the thing that is being measured.

Insights, Analysis, and Developments

Author Credentials: Ian is the founder and Editor-in-Chief of Disabled World, a leading resource for news and information on disability issues. With a global perspective shaped by years of travel and lived experience, Ian is a committed proponent of the Social Model of Disability-a transformative framework developed by disabled activists in the 1970s that emphasizes dismantling societal barriers rather than focusing solely on individual impairments. His work reflects a deep commitment to disability rights, accessibility, and social inclusion. To learn more about Ian's background, expertise, and accomplishments, visit his full biography.