Lightning Distance Calculator
Calculate the distance to lightning strikes using thunder timing and speed of sound
Calculate Lightning Distance
Count from lightning flash to thunder sound
⚠️ Safety Assessment
DANGEROUS! Seek shelter immediately. Lightning is close enough to be hazardous.
Lightning Distance
Calculation Details
Formula: Distance = Time × Speed of Sound
Speed of Sound: 343 m/s (standard at 20°C)
Time Delay: 15 seconds
⚡ 30-30 Lightning Safety Rule
30 seconds: If thunder comes within 30 seconds of lightning, seek shelter immediately
30 minutes: Wait 30 minutes after the last thunder before going outside
Current delay: 15 seconds (⚠️ DANGEROUS - Seek shelter!)
Example Calculation
Scenario: Summer Storm
Observation: Lightning flash followed by thunder
Time count: 15 seconds from flash to thunder
Temperature: 25°C (warm summer day)
Calculation Steps
1. Speed of sound at 25°C: v = 331.3 × √(298.15/273.15) = 346.1 m/s
2. Distance = 15 seconds × 346.1 m/s = 5,192 meters
3. Convert to km: 5,192 m ÷ 1000 = 5.19 km
Result: Lightning is approximately 5.2 km away
Simple rule check: 15 ÷ 3 = 5 km (very close!)
Quick Reference Rules
Distance in Kilometers
Divide seconds by 3
Example: 12 sec ÷ 3 = 4 km
Distance in Miles
Divide seconds by 5
Example: 15 sec ÷ 5 = 3 miles
Speed of Sound
≈ 343 m/s at 20°C
≈ 1,125 ft/s
≈ 1,235 km/h
Lightning Safety
Seek shelter in substantial buildings
Hard-topped vehicles are safe
Avoid trees, poles, and open areas
Stay away from water and metal objects
Avoid using electronic devices
Danger Zones
0-1 km
Immediate danger
1-8 km
High risk zone
8-16 km
Moderate risk
16+ km
Low risk (monitor)
Understanding Lightning Distance Calculation
How Does It Work?
Lightning distance calculation is based on the significant difference between the speed of light and the speed of sound. While we see lightning almost instantly, thunder takes time to reach us, allowing us to calculate the distance.
Speed Comparison
- •Light speed: 299,792,458 m/s (essentially instantaneous)
- •Sound speed: ~343 m/s at 20°C (temperature dependent)
- •Light is about 874,000 times faster than sound
Temperature Effects
The speed of sound varies with temperature because air density and molecular motion change. Higher temperatures increase molecular vibration, facilitating faster sound transmission.
Accuracy Considerations
- •Simple rules (3/5 seconds) are approximations
- •Temperature affects accuracy by ±5%
- •Humidity and altitude have minor effects
Scientific Formula
Distance = Time × Speed of Sound
v = 331.3 × √(T/273.15) m/s
Where T is absolute temperature in Kelvin
At 20°C: 343.2 m/s
At 30°C: 349.0 m/s
• Use stopwatch for accuracy
• Count "one-thousand-one" method
• Multiple measurements improve precision
• Wind can affect sound travel
• Multiple lightning strikes
• Sound reflection/echoes