10 Earnings/(loss) per ordinary share

				2017					2016
			Weighted						Weighted
			average			2017			average		2016
		2017	number of		Per share		2016		number of		Per share
	Earnings		shares		amount		Earnings		shares		amount
	US$m		(millions)		(cents)		US$m		(millions)		(cents)
Basic earnings per share attributable to ordinary
shareholders of Rio Tinto^(a)		8,762		1,786.7		490.4		4,617		1,797.3		256.9
Diluted earnings per share attributable to ordinary
shareholders of Rio Tinto ^(b)		8,762		1,799.5		486.9		4,617		1,808.6		255.3

				2015
				Weighted
				average		2015
	2015			number of		Per share
	Loss			shares		amount
	US$m			(millions)		(cents)
Basic loss per share attributable to ordinary
shareholders of Rio Tinto ^(a)		(866	)		1,824.7		(47.5	)
Diluted loss per share attributable to ordinary
shareholders of Rio Tinto^(b)		(866	)		1,824.7		(47.5	)

(a)

The weighted average number of shares is calculated as the average number of Rio Tinto plc shares outstanding not held as treasury shares of 1,364.5 million (2016: 1,373.7 million; 2015: 1,398.1 million) plus the average number of Rio Tinto Limited shares outstanding of 422.3 million (2016: 423.6 million; 2015: 426.6 million) over the relevant period. No Rio Tinto Limited ordinary shares were held by Rio Tinto plc in any of the periods presented.

(b)

For the purposes of calculating diluted earnings per share, the effect of dilutive securities of 12.8 million shares in 2017 and 11.3 million shares in 2016 is added to the weighted average number of shares described in (a) above. This effect is calculated under the treasury stock method. In accordance with IAS 33 “Earnings per share”, for the purposes of calculating diluted loss per share, the effect of potentially dilutive securities has not been taken into account for the year ended 31 December 2015. The Group’s only potential dilutive ordinary shares are share options for which terms and conditions are described in note 43.