March 11, 2026 5 min read Add Us On Google Add SciAm Iran was nowhere close to a nuclear bomb, experts say Although President Trump has claimed Iran was weeks away from developing a nuclear weapon, much more work was needed for the country to do so By Dan Vergano edited by Clara Moskowitz Tehran on March 02, 2026. Contributor/Getty Images Confusion on whether Iran truly needed only “ two weeks to four weeks ” to make a nuclear weapon, as President Donald Trump suggested on Monday, hangs over the ongoing U.S. and Israeli war on the Persian Gulf nation. Nuclear experts call this claim unlikely—but the confusion may stem from some basics of atomic chemistry. “There was no evidence that Iran was close to a nuclear weapon,” says Jeffrey Lewis of the James Martin Center for Nonproliferation Studies at the Middlebury Institute of International Studies . His comment echoed those of other experts after the war’s start, as well as statements from International Atomic Energy Agency (IAEA) chief Rafael Grossi at that time and in 2025 and last year’s “ threat assessment ” report by U.S. intelligence agencies. According to an IAEA estimate , as of June 2025, Iran possessed 441 kilograms of 60 percent enriched uranium, where the percentage refers to the share of the isotope uranium 235 (U 235) found in the material. That would be enough for 10 nuclear weapons if the material could be enriched further to full 90 percent weapons-grade concentrations, according to the IAEA. That further enrichment would take a matter of weeks in a fully functioning Iranian nuclear complex , perhaps explaining the time line within Trump’s declaration. On supporting science journalism If you're enjoying this article, consider supporting our award-winning journalism by subscribing . By purchasing a subscription you are helping to ensure the future of impactful stories about the discoveries and ideas shaping our world today. That step alone doesn’t equal a bomb, however. And Iran’s main enrichment capabilities were “completely and totally obliterated ,” according to Trump himself in June, after the U.S. bombed three underground Iranian facilities . The administration’s special envoy to the Middle East Steve Witkoff nonetheless claimed on March 3, after the start of the current war, that Iran had the capability to make 11 nuclear bombs. Trump administration officials reportedly failed to include nuclear technical experts in their negotiation teams with Iran prior to the war, adding to the uncertainty. If Iran really had rebuilt these facilities, that might have led—over months and not weeks—to the nation resuming its uranium enrichment, Lewis says. “But this is all ‘if,’ ‘maybe’ and ‘later,’” he adds. Enrichment For starters, enriching uranium isn’t simple, says former Los Alamos National Laboratory chemist Cheryl Rofer. It begins with mining uranium ore, which is then filtered and dried to make “yellowcake” uranium oxide concentrate. Yellowcake is only about 0.7 percent U 235 , where a standard atomic bomb typically requires uranium metal that is 90 percent enriched . To get there, technicians must chemically convert the yellowcake into uranium hexafluoride gas (a molecule containing one uranium atom and six fluorides) and feed it into centrifuges. Spun at 50,000 to 100,000 revolutions per minute , molecules containing the slightly lighter U 235 separate from those with the heavier, and much more common, uranium isotope U 238. The U 235 stream then travels through cascades of more centrifuges whirling to further concentrate the stream, first to 20 percent enrichment (so-called highly-enriched uranium) and then to 60 percent concentration. “It takes many stages to separate the two isotopes,” Rofer says. Since the first Trump administration withdrew from the international agreement with Iran to halt enrichment in 2018, Iran had stopped at the intermediate step of 60 percent enrichment in its production of uranium and had not proceeding to the 90 percent required for bombs. “Iran’s decision was intended to send a political message: ‘We have gone as far as we can go in response to provocations without producing weapons-grade uranium,’” noted Robert E. Kelley of the Stockholm International Peace Research Institute in 2021. Iran had buried entrances to tunnels at its Isfahan nuclear complex in February, leaving observers to conclude that the uranium remains stored, likely in canisters of uranium hexafluoride gas, or in disarray there after the June 2025 bombing of the site. To be as close as Trump claimed to having a conventional nuclear weapon, Iran would have needed to secure and enrich that gas to 90 percent in centrifuges, extract and chemically separate it back to solid uranium, shape it into spheres of uranium metal (a task that is &l