The largest empire in history in land area as a percentage of the world's land area was the British Empire
The British Empire covered 35.5 million km2 or 23.84 % of the world's land area in 1920. The biggest individual parts of it were Canada, Australia and the British Raj (India+Pakistan+Bangladesh+Myanmar). Canada and Australia were not fully independent until 1931 when the Statute of Westminster, an Act of the Parliament of the United Kingdom gave them full legislative independence from the United Kingdom.