Fledermaus.
Read the report. It breaks it all down as precisely as possible but it cannot be summarised into one easy number due to complexity. That is why I linked the whole report rather than a summary or a review.
With respect to Iraq, the US invaded that country and is therefore responsible for all deaths caused by that invasion either directly or indirectly. As the Commander in Chief of the US Armed Forces and the leader of the Executive Branch which was in charge of foreign relations and policy leading up to the war, former president George W. Bush is at the top of the chain of responsibility for all deaths (both American and Iraqi) as he is the captain of the 'ship of state' and the captain of a ship has vicarious responsibility and liability for all actions done under his command by subordinates.
https://en.m.wikipedia.org/wiki/Legitimacy_of_the_2003_invasion_of_Iraq
The USA waged unnecessary aggressive war against Iraq without explicit UN mandate which is defined as a crime against peace. US soldiers, Marines, airmen intelligence operatives and private contractors committed war crimes in Iraq. As Commander in Chief former President G. W. Bush is culpable and liable for those crimes too. So, yes, former president G. W. Bush should be indicted and tried for war crimes and crimes against peace and if found guilty he will be a war criminal.
Of course America and the US state will never let such a trial occur, so until the hypothetical day of his conviction, G. W. Bush is an alleged war criminal only.
Cheers.
Evilroddy.