Ohm's Law Calculator for Vaping
Calculate voltage, current, resistance, and power instantly. Enter any two values and get the rest. Essential for safe coil building and understanding your vape setup.
How to Use This Calculator
Identify Known Values
Determine which two values you know: voltage (V), current (I), resistance (R), or power (P).
Enter Your Values
Input your known values. For mech mods, use 4.2V (full charge). For regulated mods, check your display.
Review Results
The calculator computes the remaining values using V=IR and P=VI formulas automatically.
Check Battery Safety
Compare amp draw to your battery's CDR. Keep 20% headroom below the limit for safety.
Ohm's Law Safety Essentials
DO
- • Always calculate at 4.2V (full charge) for worst-case amp draw
- • Maintain 20% headroom below your battery's CDR
- • Verify coil resistance with an ohmmeter before firing
- • Use batteries from reputable manufacturers (Samsung, Sony, LG, Molicel)
- • Account for dual coils halving total resistance
DON'T
- • Never exceed your battery's CDR rating
- • Never use 3.7V (nominal) for safety calculations
- • Never trust rewrapped batteries (Efest, MXJO, Imren) at face value
- • Never build below 0.1Ω without expert knowledge
- • Never ignore unstable resistance readings
Minimum Safe Resistance by Battery CDR
At 4.2V (fully charged), here's the minimum safe resistance for common battery ratings:
| Battery CDR | Min Resistance | With 20% Headroom | Example Batteries |
|---|---|---|---|
| 15A | 0.28Ω | 0.35Ω | Samsung 30Q |
| 20A | 0.21Ω | 0.26Ω | Samsung 25R, LG HG2 |
| 25A | 0.17Ω | 0.21Ω | Sony VTC5A, Molicel P26A |
| 30A | 0.14Ω | 0.18Ω | Samsung 20S, Molicel P42A |
Formula: Minimum Resistance = 4.2V ÷ Battery CDR. For dual coils, double the minimum resistance.
Common Ohm's Law Mistakes
Using 3.7V Instead of 4.2V
3.7V is nominal voltage. Always use 4.2V (full charge) to calculate maximum amp draw for safety.
Forgetting Dual Coils
Two 0.4Ω coils in parallel = 0.2Ω total. This doubles your amp draw compared to a single coil.
Series Mod Confusion
Series doubles voltage to 8.4V, which also doubles amp draw. A 0.25Ω build draws 33.6A - too high for most batteries.
Trusting Fake CDR Ratings
No 18650 has a true CDR over 30A. "40A" claims on rewrapped batteries are pulse ratings, not continuous.
Building at Exact CDR Limit
Always keep 20% headroom. At the exact limit, any measurement error or battery degradation becomes dangerous.
Regulated ≠ Mech Math
Regulated mods adjust voltage automatically. Use the Battery Safety Calculator for regulated mod amp draw.
Understanding Ohm's Law for Vaping
Ohm's Law is the foundation of electrical understanding in vaping. It describes how voltage, current, resistance, and power relate to each other. For vapers, especially those using mechanical mods or building their own coils, understanding these relationships is crucial for both performance and safety.
The Key Formulas
Voltage (V)
V = I × R
Voltage equals current times resistance. Higher resistance needs more voltage for the same current.
Current (I)
I = V / R
Current equals voltage divided by resistance. Lower resistance draws more current.
Resistance (R)
R = V / I
Resistance equals voltage divided by current. Your coil's resistance determines current draw.
Power (P)
P = V × I = I²R = V²/R
Power (wattage) is what heats your coil. More power = more heat = more vapor.
Why This Matters for Vapers
- Battery Safety: Knowing current draw helps confirm you don't exceed your battery's CDR
- Mechanical Mods: Mech mods don't regulate power - Ohm's Law is your only guide
- Coil Building: Understanding resistance helps you build coils that perform as expected
- Troubleshooting: When something isn't working right, Ohm's Law helps diagnose issues
Frequently Asked Questions
What is Ohm's Law?
Ohm's Law describes the relationship between voltage (V), current (I), and resistance (R). The formula is V = I × R. In vaping, this helps you understand how your coil resistance affects power output and battery draw.
Why is Ohm's Law important for vaping?
Understanding Ohm's Law is crucial for vape safety, especially with mechanical mods. It helps you calculate how much current your battery needs to supply, verify you're within safe limits, and find the right wattage for your build.
How do I use the Ohm's Law calculator?
Enter any two values (voltage, current, resistance, or power) and the calculator will solve for the other two. For example, if you know your battery voltage (4.2V) and coil resistance (0.5Ω), it will calculate current draw and power output.
What voltage should I use for vaping calculations?
For regulated mods, use the voltage your mod outputs (check your display). For mechanical mods, use 4.2V (fully charged) for maximum amp draw or 3.7V (nominal) for average calculations.
What's a safe current draw for vape batteries?
Stay within your battery's CDR (Continuous Discharge Rating). Most 18650 batteries are rated 15-30A. Always leave a 20% safety margin. Use our Battery Safety Calculator for detailed analysis.