Blast Radius Calculator finds the minimum safe distance from an explosive by its weight, for bare, cased or lined-up items, under UN range formulas. It also checks where you stand.
All-up weight of the ammunition or bare explosive, as the UN range safety formulas use it.
Result Unit
Safe Distance Rings
Calculation Steps
- Root of the weight: W^(1/3) = 0.5^(1/3) = 0.7937
- Safe distance: D = 130 × 0.7937 = 103.2 m
- Margin: 150 m − 103.2 m = 46.82 m
- Safe distance: 103.2 m, and you are outside it
Safe Distance by Weight
| Weight | Bare | In a Line | Cased |
|---|---|---|---|
| 0.1 kg | 60.34 m | 233.5 m | 431.9 m |
| 0.5 kg | 103.2 m | 322.1 m | 564.8 m |
| 1 kg | 130 m | 370 m | 634 m |
| 5 kg | 222.3 m | 510.5 m | 829.1 m |
| 10 kg | 280.1 m | 586.4 m | 930.6 m |
| 50 kg | 478.9 m | 809.1 m | 1,217 m |
| 100 kg | 603.4 m | 929.4 m | 1,366 m |
| 500 kg | 1,032 m | 1,282 m | 1,786 m |
| 1,000 kg | 1,300 m | 1,473 m | 2,005 m |
Each figure is the distance outside which no more than one fragment is expected to fly. None is absolutely safe. Cased and in-a-line figures are never below the bare one.
Storage Separation by Z
| Z | From a Storehouse to | Distance |
|---|---|---|
| 8 | Process buildings in a storage area | 6.35 m |
| 14.8 | Public traffic route | 11.75 m |
| 22.2 | Inhabited building | 17.62 m |
| 44.4 | Vulnerable building, such as a school | 35.24 m |
| 189 | Your distance | 150 m |
Blast separation for stored explosives, from Table 2 of IATG 01.80. Minimum distances also apply and differ for each Z.
What the Blast Radius Calculator Gives
The Blast Radius Calculator works out the minimum distance to keep people back from an explosive charge. It uses the range safety formulas in the United Nations ammunition guideline IATG 01.80. With the loaded 0.5 kg of bare explosive the safe distance is 103.2 m.
The second field takes your own distance and checks it against that line. At 150 m you are 46.82 m outside it. Switch the Situation to a cased munition and the line moves out to 564.8 m, which leaves the same 150 m well inside the danger area. A Solve For choice turns the question around and gives the largest weight a set distance allows.
The UN defines this distance as the one outside which no more than one fragment would be expected to fly. The guideline states that the distances are not absolutely safe. Treat every figure as a minimum for planning a cordon, never as a promise that the ground beyond it is harmless.
How to Calculate Blast Radius
To calculate the blast radius of a charge, take a root of its weight in kilograms and multiply by a constant. The weight is the all-up weight, which means the whole item including any casing. The UN gives one formula for each of three situations.
$$D = 130 \times W^{1/3}$$
This is the formula for bare exposed explosive with no casing. D is the distance in meters and W is the all-up weight in kilograms. For 1 kg the cube root is 1, so the safe distance is 130 m.
$$D = 634 \times W^{1/6}$$
This one covers a fragmenting munition where the public could have access. The sixth root rises slowly, so the distance starts large and grows little. One kilogram already needs 634 m.
$$D = 370 \times W^{1/5}$$
The third formula is for several items laid in a line and fired together. The guideline takes it from Australian research on multi-item demolitions. It assumes a row of items, not a stack, with each more than one charge diameter from the next.
| All-up weight | Bare explosive | Items in a line | Cased munition |
|---|---|---|---|
| 0.1 kg | 60.34 m | 233.5 m | 431.9 m |
| 0.5 kg | 103.2 m | 322.1 m | 564.8 m |
| 1 kg | 130 m | 370 m | 634 m |
| 5 kg | 222.3 m | 510.5 m | 829.1 m |
| 10 kg | 280.1 m | 586.4 m | 930.6 m |
| 50 kg | 478.9 m | 809.1 m | 1,217 m |
| 100 kg | 603.4 m | 929.4 m | 1,366 m |
| 500 kg | 1,032 m | 1,282 m | 1,786 m |
| 1,000 kg | 1,300 m | 1,473 m | 2,005 m |
The table is the Safe Distance by Weight table from the tool. Weight can go in as kilograms, grams, pounds, metric tons or US tons, and the answer can be shown in meters, feet, yards, kilometers or miles.
Why a Casing Raises the Distance
A high blast radius for a small weight nearly always comes from fragments. The pressure wave from bare explosive fades fast with distance. Pieces of a steel casing keep flying long after the blast itself has become harmless.
That is why 1 kg needs 130 m when bare and 634 m when cased. The gap narrows as the weight grows, because the two formulas use different roots. At 1,000 kg the bare distance is 1,300 m and the cased distance is 2,005 m.
The first result card always shows the other two situations beside the one you picked. It also shows the distance at ten times the weight. For 0.5 kg of bare explosive, ten times the weight raises the line from 103.2 m to 222.3 m, which is only a little more than double.
At very large weights the formulas cross. For 3 t laid in a line the fragment formula gives 1,835 m, which is less than the 1,875 m for bare explosive. The tool then shows 1,875 m and marks it “Blast governs”. That rule is the tool’s own, and it only ever lengthens the distance.
Blast Radius of Bombs and Shells by Weight
Questions about the blast radius of a 500 kg bomb or a 1000 lb bomb are answered here in the same way, as safety distances. A bomb or shell is a cased munition, so the cased column applies. The bare column is listed for comparison, and for a ton of TNT with no casing.
| All-up weight | Bare explosive | Cased munition |
|---|---|---|
| 500 lb (226.8 kg) | 792.8 m | 1,566 m |
| 1,000 lb (453.6 kg) | 998.8 m | 1,757 m |
| 500 kg | 1,032 m | 1,786 m |
| 1 US ton (907.2 kg) | 1,258 m | 1,973 m |
| 1 metric ton | 1,300 m | 2,005 m |
| 3 metric tons | 1,875 m | 2,408 m |
So the blast radius of 1 ton of TNT, as bare explosive, is 1,300 m for a metric ton and 1,258 m for a US ton. Three tons of TNT calls for 1,875 m, and the area to clear around it is 1,104 hectares. A 500 lb bomb needs 1,566 m and a 500 kilo bomb 1,786 m under the cased formula.
These are clearance distances, and they are far larger than the zone of heavy damage that news reports often call the blast radius. The formulas are written for the rare fragment that travels farthest, since a single one can kill.
For an artillery round, a mortar bomb or a missile warhead, enter the all-up weight from the ammunition data in the Blast Radius Calculator and keep the cased setting. A 5 kg item needs 829.1 m, a 10 kg item 930.6 m and a 50 kg item 1,217 m. The size of the gun matters only through the weight of what it fires.
Largest Weight for a Distance
Sometimes the distance is fixed and the weight is the unknown. Set Solve For to the largest weight, enter the distance you can keep clear, and the Blast Radius Calculator inverts the formula for the chosen situation.
$$W = \left(\frac{D}{130}\right)^3$$
This is the bare explosive case, and the cased and in-a-line cases invert their own formulas in the same way. With 150 m kept clear, the limit is 1.536 kg of bare explosive, or 3.387 lb. Doubling the distance to 300 m raises the limit eight times, to 12.29 kg.
| Distance kept clear | Bare explosive | Items in a line | Cased munition |
|---|---|---|---|
| 100 m | 455.2 g | 1.442 g | 0.0154 g |
| 200 m | 3.641 kg | 46.15 g | 0.9855 g |
| 500 m | 56.9 kg | 4.507 kg | 240.6 g |
| 1,000 m | 455.2 kg | 144.2 kg | 15.4 kg |
| 2,000 m | 3.641 t | 3.641 t | 985.5 kg |
The cased column shows how strict the fragment formula is. A cordon of 200 m covers less than one gram of cased munition, so any real cased item needs several hundred meters. At 1,000 m the limit is still only 15.4 kg.
Area, Cordon and Airspace
The second card of the Blast Radius Calculator turns the safe distance into ground to clear. A 103.2 m radius covers 3.345 hectares, or 8.265 acres, and needs 648.3 m of cordon to close the circle. At the cased distance of 564.8 m the area grows to 100.2 hectares.
The third card gives the vertical danger height from a separate UN formula, 314 times the cube root of the weight for a single item. For 0.5 kg that is 249.2 m, shown as 817.7 ft for air traffic. Items in a line use 470 times the fifth root, which gives 409.2 m for the same weight.
The same card shows where the bang drops to 140 dB, which the guideline treats as the critical level for impulse noise. The formula is 215 times the cube root of the explosive mass, or 170.6 m for 0.5 kg. The card treats all the weight as explosive, so for a cased item the noise line errs on the long side.
People who search for a blast radius calculator map want to see the circle on the ground. The tool draws the three rings to scale in a top view, with your position marked. To place them on a real map, draw a circle of the safe distance around the charge in any mapping app.
Scaled Distance in Blast Physics
The physics behind every blast radius calculator is the Hopkinson-Cranz scaling law. Two charges of the same explosive give the same blast pressure at the same scaled distance, which is the distance divided by the cube root of the weight.
$$R = Z \times W^{1/3}$$
R is the range in meters, W is the explosive weight in kilograms and Z is a constant set by the pressure that can be accepted. The fourth card gives the Z of your own position. Standing 150 m from 0.5 kg is a scaled distance of 189.
The UN guideline uses four Z values for separating stored explosives from their surroundings. The last accordion in the tool applies them to your weight. For a storehouse holding 1,000 kg the distances come out as below, and the guideline adds minimum distances that differ for each Z.
| Z | From a storehouse to | Distance for 1,000 kg |
|---|---|---|
| 8.0 | Process buildings in a storage area | 80 m |
| 14.8 | Public traffic route | 148 m |
| 22.2 | Inhabited building | 222 m |
| 44.4 | Vulnerable building, such as a school | 444 m |
A blast damage calculator goes one step further and turns Z into a pressure. The US government’s Radiation Emergency Medical Management site lists 5 psi as the level that injures eardrums and 15 psi as the level that injures lungs. This tool stops at Z and distance and does not estimate pressure.
TNT, C4 and RDX Weights
One kilogram of TNT releases 4.184 MJ, and one gram releases 4,184 J. A kiloton of TNT is 4.184 × 10¹² J. As bare explosive, 1 kg of TNT has a safe distance of 130 m and a 140 dB line at 215 m, while a single gram still needs 13 m.
RDX is more powerful than TNT weight for weight. The UN guideline lists RDX at 1.14 to 1.15 times TNT, Composition B at 1.09 to 1.11 and C4 at 1.13 to 1.37, depending on the method used. It also warns that TNT equivalence is not precisely defined.
The range formulas use the all-up weight as it stands, so a C4 blast radius calculator and a TNT explosion calculator share the same three formulas. To compare the blast energy of different fillings, convert the weight first with the TNT Equivalent Calculator.
What are the three types of explosives?
US federal rules sort explosive materials into three classes. Title 27, section 555.202 lists high explosives such as dynamite, low explosives such as black powder, and blasting agents such as ammonium nitrate-fuel oil. High explosives detonate, while low explosives burn rapidly when confined.
Nuclear and Game Blast Radius
What is the safe distance from a nuclear bomb?
There is no single safe radius for a nuclear blast. The reach depends on the yield, the height of the burst and the wind that carries the fallout. The formulas in this tool are for conventional ammunition weighed in kilograms, so it is not a nuclear blast radius calculator.
Distance from the blast is also only part of the danger. The Radiation Emergency Medical Management site notes that fallout can land miles upwind as well as downwind. It also shows fallout radiation dropping to about 10% of its first level after 8 hours and 1% after 48 hours, and it advises sheltering for at least 24 hours when possible.
Blast radius of TNT in Minecraft
Minecraft TNT follows game rules, not physics. A TNT block has an explosion power of 4 and a fuse of 80 game ticks, which is 4 seconds. Its reach is counted in blocks and has no link to the UN formulas, so real distances for TNT come from the weight tables above.