Bombs Over Cambodia, also known as "The Walrus" Article by Ben Kiernan and Taylor Owen.

Here is an attempt to correct some numbers, in 2006 Kiernan wrote in an article for "The Walrus", that according to some estimates they could calculate that there were more than 2.5 million tons of ordinance dropped on Cambodia from 1965-1973.

Four years later, they corrected this number because they had used 'mistaken technical analysis'. They had miscalculated by about 5 times (if my maths is correct). From 2.5 million tons, this was reduced to 500,000 tons. 

This is detailed in this article in the Asia Pacific Journal, by Kiernan https://apjjf.org/Ben-Kiernan/4313.html 

Here is the relevant quote from Kiernan:

During 2000-2010 various estimates, including ours, of the U.S. bombing tonnage dropped on Cambodia from 1969 to 1973 followed a trajectory similar to High’s up-down estimates for Laos. And for similar reasons: the difficulties of technical analysis of the Pentagon’s enormous but antiquated Southeast Asia bombing databases. In 1989 one of us (Kiernan) had published an article calculating a figure of 539,000 tons dropped on Cambodia.13 But in 2000, just as High did for Laos eight years later, the Phnom Penh Post reported a new Cambodia total, a dramatic upward revision: “The [data] tapes show that 43,415 bombing raids were made on Cambodia dropping more than 2 million tons of bombs and other ordinance.”14 This figure had significant implications for the continuing work to clear the Cambodian countryside of the still widespread, deadly unexploded ordnance (UXO), as well as for a historical understanding of the wartime humanitarian and political impact of the US carpet bombings.
Our 2006 article, “Bombs over Cambodia,” using the same database and analysis, calculated a figure of 2.7 million tons dropped on Cambodia in 1965-75.15 Our estimate, published in the Canadian magazine The Walrus, and in 2007 in The Asia-Pacific Journal, was widely quoted.
But in 2010 we corrected that estimate, here in The Asia-Pacific Journal. We revised it back down to around 500,000 tons.17 In doing so we took account of the mistaken technical analysis that had impacted bombing tonnage estimates for both Laos and Cambodia. Holly High had written to Kiernan on January 4, 2010: “I have been working with computer scientists here at Sydney and we have managed to make a fairly responsive database and also account for the anomalies in the data . . . The database covers all of Southeast Asia, and contains many more fields than the data that you were working with, from what I can tell from the data on the Cambodian Genocide Project website. It looks like the data you and others in the UXO business were provided with was a simplified, distilled version of the original SEADAB and CACTA files [combined Pentagon databases entitled “Records About Air Sorties Flown in Southeast Asia,” and “Combat Air Activities”], sorted country by country so that each nation received only “its” records. The original database is much larger: indeed it is simply massive. It is also deeply flawed (some of the data appears to have been corrupted and there are omissions in certain months).”
Kiernan wrote back to High on January 18, 2010 stating that “we would urgently like to incorporate corrections of mistakes that were based on faulty Pentagon data, and show where that data is inaccurate. If it is okay with you, we would of course like to credit you and your skilled research assistant at Sydney Uni’s Faculty of Information Technology, who has worked on this with you, for bringing the database errors to our attention. Obviously the sooner we correct those the better.” In an email of March 1, 2010, High asserted that in the Pentagon’s SEADAB database, the original entries for each sortie under the field of bombing “Load Weight” had been incorrectly keyed in, with a zero mistakenly added to each figure. Those bombing tonnages thus had to be divided by ten.
In June 2010, therefore, we published our downward correction of our 2006 estimate of 2.7 million tons. We stated that “this tonnage data may be incorrect. In new work using the original Air Force SEADAB and CACTA databases, Holly High and others have re-analyzed the total Cambodia tonnage figures and argue in a forthcoming article that the total tonnage dropped on Cambodia was at least 472,313 tons, or somewhat higher.” We concluded: “It remains undisputed that in 1969-73 alone, around 500,000 tons of U.S. bombs fell on Cambodia.”
I'm writing this blog post about it in the hopes that the original figure is no longer casually shared, because as Kiernan says, it often is... but this correction is rarely sought out or provided.