A nuclear weapon's destructive effects extend far beyond the initial fireball. A 1-megaton warhead creates a fireball nearly a mile wide, thermal burns out to 7 miles, blast damage strong enough to demolish residential buildings out to 4 miles, and potentially lethal radiation fallout extending 50+ miles downwind. This calculator maps these concentric zones of destruction based on weapon yield, detonation altitude, and your distance from ground zero. While it was designed for civil defense education and awareness, the physics are based on published nuclear effects research and blast modeling from sources like the Nuclear Weapons Effects Calculator used by defense planners.
Nuclear Blast Radius Calculator
How to Use This Calculator
- Select the weapon yield — from tactical weapons of a few kilotons to strategic warheads of several megatons
- Choose airburst or ground detonation — airbursts maximize blast damage while ground bursts create more fallout
- Enter a location or distance to see which effect zones you fall within
- View the fireball radius, severe blast damage zone, moderate damage zone, thermal radiation zone, and initial radiation zone
- Understand the fallout zone for ground bursts, which extends primarily downwind
How It Works
This nuclear blast radius calculator uses established formulas to provide accurate results.
The basic rule:
- Blast radii scale with the cube root of yield: R = k × Y^(1/3)
- 20 psi overpressure: total destruction; 5 psi: severe damage; 1 psi: window breakage
- Thermal radiation travels at the speed of light — no warning time at close range
Results are estimates based on standard formulas. Verify with current local data for your specific situation.
Tips & Considerations
- The majority of nuclear weapons in current arsenals are in the 100-500 kiloton range — not the massive multi-megaton weapons of the Cold War era.
- Airburst detonations (optimized for a specific altitude) cause wider blast damage but minimal fallout. Ground bursts cause localized destruction plus extensive radioactive fallout.
- A single concrete building provides meaningful protection from initial radiation and thermal effects. Getting indoors within 15 minutes of a detonation significantly improves survival odds.
- Modern nuclear strategy focuses on counterforce targets (military installations) rather than countervalue targets (cities), though either scenario would be catastrophic.
Frequently Asked Questions
How big is the blast radius of a nuclear bomb?
The blast radius depends heavily on yield. The Hiroshima bomb (15 kilotons) had a severe destruction radius of about 1 mile and caused damage out to 4-5 miles. A modern strategic warhead (800 kilotons) would have a severe destruction radius of about 3 miles and cause damage out to 12-15 miles. The largest weapon ever tested, the Tsar Bomba (50,000 kilotons), had a damage radius of roughly 35 miles.
What is the difference between airburst and surface burst?
An airburst detonation (hundreds of meters above ground) maximizes the blast wave's destructive area because the reflected wave combines with the direct wave. Surface bursts create a smaller blast radius but produce enormous amounts of radioactive fallout because ground material is vaporized and irradiated, then carried downwind. Military targets in the open are typically airburst; hardened targets like bunkers use surface burst.
How far away do you need to be to survive a nuclear blast?
For a Hiroshima-sized weapon (15 kt), being 2+ miles away gives a reasonable chance of survival in a sturdy building. For a modern strategic warhead (500-800 kt), you would want to be at least 8-10 miles away. However, even beyond the blast radius, radioactive fallout from surface bursts can be lethal at much greater distances. Sheltering indoors for 24-72 hours after detonation dramatically reduces fallout exposure.
What should you do if a nuclear bomb goes off?
If you see a flash: do not look at it (flash blindness). Get inside the nearest substantial building immediately. Move to interior rooms, basement, or center of building. Close all windows and doors, turn off ventilation. Stay sheltered for at least 24 hours — radiation levels drop by 80% after the first day. After 2 weeks, outdoor radiation drops to about 1% of initial levels. Have water, food, and a battery-powered radio.
Could you survive a nuclear bomb in a basement?
A basement significantly improves survival odds outside the severe blast zone. Concrete and earth provide excellent radiation shielding — a basement reduces radiation exposure by a factor of 10-20 compared to being outdoors. At moderate damage distances (2-5 miles for a 15 kt weapon), a basement in a sturdy building could absolutely save your life. The main risks are building collapse from the blast wave and subsequent fires. Stay away from windows and exterior walls.