About 140,000 people are estimated to have died in Hiroshima by the end of December 1945, give or take 10,000 — the official estimate of the city's Peace Memorial Museum. [1, 2] In Nagasaki more than 70,000 died, with a city report putting the end-of-1945 toll at 73,884 killed. [3, 4] The exact numbers will never be known, as both cities say; the figures below are the best-sourced estimates, shown with the definition each one uses.
The death toll in each city
There is no single official death toll, because the deaths were counted in different ways. The most-cited figures are the number of deaths by the end of 1945 and the Radiation Effects Research Foundation's estimate of acute deaths within two to four months of the bombings.
| City | Deaths by end of 1945 | Acute deaths within 2–4 months (RERF) |
|---|---|---|
| Hiroshima | About 140,000 (±10,000) [1, 2] | 90,000–166,000 [5] |
| Nagasaki | 73,884 killed; 74,909 injured [4] | 60,000–80,000 [5] |
The US National Park Service describes "eighty thousand killed or grievously wounded instantly" at Hiroshima and "over 100,000 more in the coming months." [6] Those figures combine deaths and injuries, so they are not a death count and should not be added together. Both cities also keep a register of the names of the dead — 353,639 names at Hiroshima by August 2026 and 202,053 at Nagasaki — but these are cumulative lists of names added on application over 80 years, not a tally of deaths in 1945. [7, 8, 9]
When the bombs were dropped
Hiroshima was bombed at 8:15 a.m. on 6 August 1945. The B-29 Superfortress Enola Gay, commanded by Colonel Paul W. Tibbets, Jr., dropped Little Boy, a 15-kiloton gun-type uranium bomb; [10, 6, 11, 12] it exploded 43 seconds later, about 600 m above the city. [13]
Nagasaki was bombed at 11:02 a.m. on 9 August 1945. The B-29 Bockscar, commanded by Major Charles W. Sweeney, dropped Fat Man, a 21-kiloton implosion-type plutonium bomb, [3, 6, 12] which detonated about 503 m above the Urakami district. [5] Both weapons were air bursts, detonated high above the ground to spread the blast, so neither city received heavy local fallout.
Why the US bombed Hiroshima
The stated justification was to end the war without an invasion of Japan. The Potsdam Declaration of 26 July 1945 warned Japan of "prompt and utter destruction" if it did not surrender. [14] Announcing the bombing on 6 August, President Truman called Hiroshima "an important Japanese Army base," said the Potsdam ultimatum had been issued "to spare the Japanese people from utter destruction," and framed the attack as an answer to Pearl Harbor: "They have been repaid many fold." [15]
Nagasaki was not the intended target on 9 August. The primary target was Kokura; the Bockscar crew turned to the secondary target, Nagasaki, after the primary was obscured. Sources differ on the obscurant — Nagasaki City records smoke, the National Park Service haze, and the US Air Force museum clouds. [16, 6, 17] This page describes the history in neutral terms and takes no view on whether the bombings were justified.
The survivors
As of the end of March 2026, 91,105 survivors of the bombings were still living, with an average age of 86.66. [18] The count is the number of holders of the Atomic Bomb Survivor's Health Handbook issued by Japan's Ministry of Health, Labour and Welfare; it fell below 100,000 for the first time the previous year. [19] The survivors are known in Japanese as hibakusha. The ministry updates the figure each year in July, so it is rechecked annually.
Are Hiroshima and Nagasaki radioactive today?
No — not at any level that affects health. RERF's answer to whether the cities are still radioactive is, in its words, "The practical answer is, 'No.'": the residual radioactivity is now so small it is hard to distinguish from the trace fallout found worldwide, and most of the neutron-induced activity decayed within a day. [5] The City of Hiroshima puts present-day radiation "on a par with extremely low background levels," with no effect on the body. [20] Both cities were rebuilt and are home to well over a million people between them.
What 80 years of RERF data show
Hiroshima and Nagasaki produced the only large datasets on nuclear-weapon effects in real cities, and 80 years of follow-up has shaped modern radiation safety. The Atomic Bomb Casualty Commission began studying survivors in 1947 and was reorganized as the Radiation Effects Research Foundation in 1975. [21] Its Life Span Study tracks roughly 120,000 people and underpins essentially all modern radiation-protection standards. [22]
The data established the dose-response relationship for radiation-induced cancer: survivors with high doses had clearly elevated rates of leukemia, which rose about two years after exposure and peaked six to eight years later, and of solid cancers, whose excess risk persisted for life. [23] It also showed that some feared effects did not appear — no detectable increase in genetic abnormalities in survivors' children. The foundational figure for acute radiation syndrome, the dose that kills about half of those exposed within 60 days, is roughly 2.5 to 5 gray. [24]
These were the only two nuclear weapons ever used in war, [25] and both were small by modern standards at 15 and 21 kilotons. [12] No nuclear weapon has been used in war since 9 August 1945. [26] You can see the blast radii of each bomb on the Little Boy and Fat Man pages.