Chronology of Top Ten Most Populous Nations Metrication:

India is projected to surpass China as nation with highest human population while populations of Japan and Russia are steadily declining.

Top Ten Most Populous Nations (United Nations Estimates)

237 BRA Brazil

BRA Capital Time Zone -3 Brasil Brasilia
Metric System Adoption: 1814 and 1862; see MetricPioneer.com/Brasil for more detail
Compulsory Metric Implementation: 1874
United Nations Member: 24 Oct 1945

197 MEX Mexico

MEX Capital Time Zone -6 México (Mexico) Ciudad de México (Mexico City)
Metric System Adoption: 1857
Compulsory Metric Implementation: 1896
United Nations Member: 7 Nov 1945
Note: International paper size A4 is the established ISO standard adopted by all countries in the world (except the United States and Canada) as well as the official United Nations document format size. Mexico, Costa Rica, Colombia, Venezuela, Chile and the Philippines are places where the US Letter Format is still in common use, despite their official adoption of the ISO standard.

44 RUS Russia

RUS Capital Time Zone +3 Росси́я (Russia) Москва (Moscow)
Metric System Legal: 1899
Metric System Adoption: 1918
Compulsory Metric Implementation: 1927
United Nations Member: 24 Oct 1945

20 CHN China

CHN Time Zone +8 China Beijing
Metric System Legal: 1908; see MetricPioneer.com/China for more detail
Metric System Adoption: 1929
Compulsory Metric Implementation: 1930
United Nations Member: 24 Oct 1945

47 IND India

IND Time Zone +5.5 Bharat (India) New Delhi
Metric System Legal: 1920
Metric System Adoption: 1954
Compulsory Metric Implementation: 1956; see MetricPioneer.com/India for more detail
United Nations Member: 30 Oct 1945

34 IDN Indonesia

IDN Time Zone +7, +8, +9 Indonesia Jakarta
Metric System Adoption: 1923
Compulsory Metric Legislation: 1938
United Nations Member: 28 Sep 1950

104 PAK Pakistan

PAK Time Zone +5 Pakistan Islamabad
International System Adoption: 1967-72
United Nations Member: 30 Sep 1947

78 NGA Nigeria

NGA Time Zone +1 Nigeria Abuja
International System Adoption: 1971-73
United Nations Member: 7 Oct 1960
Member of ECOWAS

43 BGD Bangladesh

BGD Time Zone +6 Bangladesh Dhaka
International System Legal Adoption: 1982
Compulsory Metric Implementation: 1982
United Nations Member: 17 Sep 1974

196 USA United States of America

USA Capital Time Zone -5 United States of America Washington, DC (District of Columbia)
Metric System Legal: 1866
International System Adoption: Incomplete
Compulsory Metric Implementation: ____
United Nations Member: 24 Oct 1945

Population Projection Rank 11 to 20

Click on the image of Earth here to see when metrication occurred in each country or territory on Earth:

Population of the Thirteen Colonies and the United States