Calculate blast overpressure zones, damage radii, and fireball size for explosions using Hopkinson-Cranz scaling. Educational physics tool.
The **Blast Radius Calculator** estimates the overpressure damage zones from an explosion using Hopkinson-Cranz cube-root scaling and simplified Kingery-Bulmash blast parameters. This is a standard engineering tool used in safety analysis, building design near explosive hazards, and munitions effects evaluation.
Given the TNT-equivalent yield, burst type (surface or free-air), and atmospheric conditions, the calculator returns the radii for heavy structural damage, moderate damage, light damage, and glass breakage. It also computes the overpressure at any specified distance, the fireball radius, and the total blast energy.
This tool is intended for **educational and engineering safety** purposes — understanding safe standoff distances, designing blast-resistant structures, and teaching the physics of shock-wave propagation. All results are approximate; real-world blast effects depend on terrain, structures, confinement, reflections, and fragment distribution. Use it to compare scenarios and understand order-of-magnitude effects rather than as a substitute for a formal blast assessment. It is best treated as a first-pass screening tool that helps frame the right standoff question before a specialist model is used.
Blast effects do not scale intuitively, and rough mental estimates can be badly misleading when comparing different charge sizes or standoff distances. This calculator gives a structured way to compare overpressure zones, point overpressure, and fireball size using standard scaling laws so engineers and students can discuss the same assumptions from the start.
Cube-Root Scaling: Z = R / W^(1/3) Damage radii scale as R ∝ W^(1/3) × K (constant for each overpressure level) Total Energy: E = W × 4.184 MJ/kg Surface Factor: ×1.8 (ground reflection / Mach stem amplification) Simplified Kingery-Bulmash overpressure used for the distance profile.
Result: Heavy damage ≈ 18 m, moderate ≈ 31 m, light ≈ 83 m, glass ≈ 126 m
A 1-tonne TNT surface burst produces heavy structural damage (~10 psi) within about 18 m, and glass breakage out to ~126 m. At 100 m, overpressure is approximately 2.5 kPa (0.36 psi).
The zone labels are shorthand for overpressure ranges, not guarantees of a specific outcome. Heavy, moderate, and light damage bands help compare relative severity, but real structures respond differently depending on materials, orientation, openings, and reflected pressure. Use the zones as screening thresholds and then move to a dedicated structural review if the stakes are high.
Hopkinson-Cranz scaling is a good first-order model for open-air blasts, but it does not capture every real-world effect. Confinement, nearby walls, urban reflections, partial shielding, and unusual charge geometry can all shift the pressure field. That is why the calculator is most useful for education, standoff comparisons, and early safety checks rather than final design approval.
Overpressure is only one part of the picture. Fragments, thermal radiation, crater effects, and secondary debris can extend the dangerous area well beyond the pressure zone shown here. If you are reviewing a real hazard scenario, treat this output as one layer in a broader safety analysis.
A standard measure of explosive energy. 1 kg TNT = 4.184 MJ. Using TNT equivalent makes different explosive scenarios easier to compare on the same energy scale.
When the blast wave reflects off the ground and merges with the incident wave, it forms an amplified shock front called a Mach stem. That is why surface bursts can produce stronger ground-level overpressure than free-air bursts of the same yield.
They are useful for open-terrain screening and education, but actual blast effects vary with confinement, elevation, obstacles, and atmospheric conditions. Treat the numbers as approximate standoff guidance, not a detailed site-specific prediction.
Human injury thresholds are approximate and depend on exposure and shielding. Eardrum rupture is often discussed around 5 psi, serious lung injury around 15 psi, and life-threatening effects at still higher pressures.
Hopkinson-Cranz scaling: similar blast effects occur at distances proportional to the cube root of the yield. Doubling the yield only extends the damage radius by 26%.
No. Fragment range can far exceed the blast damage radius for cased explosives. If fragmentation is important, it needs to be assessed separately from overpressure.