Coil & Ohm's Law Calculator
Calculate coil resistance, solve Ohm's Law problems, and verify your build is safe for your batteries. Essential for coil builders and advanced vapers.
How to Use This Calculator
This calculator has three modes to help you build safe coils:
Ohm's Law
Enter any 2 values (Voltage, Current, Resistance, Power) and calculate the rest. Lock your known values using the lock icons.
Coil Builder
Select wire material, gauge, and coil dimensions to calculate resistance and recommended wattage ranges.
Battery Safety
Verify your build is within your battery's CDR (Continuous Discharge Rating) before use.
Wire Reference Tables
Wire Materials ReferenceResistivity values are at room temperature (20°C)
| Material | Resistivity | TC Mode | Notes |
|---|---|---|---|
| Kanthal A1 | 1.45 Ω·mm²/m | No | Most popular. Great for beginners, wattage mode only. |
| Kanthal A | 1.39 Ω·mm²/m | No | Similar to A1, slightly lower resistance. |
| Kanthal D | 1.35 Ω·mm²/m | No | Lower resistance Kanthal variant, faster ramp-up. |
| Nichrome N80 | 1.09 Ω·mm²/m | No | Fast ramp-up, popular for flavor builds. |
| Nichrome N60 | 1.11 Ω·mm²/m | No | 60% nickel nichrome, slightly higher resistance than N80. |
| Nichrome N70 | 1.08 Ω·mm²/m | No | 70% nickel nichrome, balanced properties. |
| SS316L | 0.75 Ω·mm²/m | Yes | Most popular SS. Works in wattage and TC modes. |
| SS304 | 0.71 Ω·mm²/m | Yes | Common food-grade SS, slightly lower resistance than 316L. |
| SS317L | 0.79 Ω·mm²/m | Yes | Higher molybdenum content, corrosion resistant. |
| SS430 | 0.60 Ω·mm²/m | Yes | Ferritic SS, magnetic, good for TC. |
| Nickel Ni200 | 0.10 Ω·mm²/m | Yes | TC MODE ONLY - Do not use in wattage mode |
| Titanium Grade 1 | 0.54 Ω·mm²/m | Yes | TC MODE ONLY - Releases toxic oxide above 650°C |
| Titanium Grade 2 | 0.56 Ω·mm²/m | Yes | TC MODE ONLY - Releases toxic oxide above 650°C |
| NiFe30 (Resistherm) | 0.32 Ω·mm²/m | Yes | TC MODE ONLY - Advanced users |
| NiFe48 | 0.48 Ω·mm²/m | Yes | TC MODE ONLY - Advanced users |
Wire Gauge Reference (AWG)
| AWG | Diameter (mm) | Typical Use |
|---|---|---|
| 20 AWG | 0.812 mm | Low resistance, high power builds |
| 22 AWG | 0.644 mm | Low resistance, high power builds |
| 24 AWG | 0.511 mm | General purpose |
| 26 AWG | 0.405 mm | Versatile, popular for most builds |
| 28 AWG | 0.321 mm | Versatile, popular for most builds |
| 30 AWG | 0.255 mm | MTL, high resistance builds |
| 32 AWG | 0.202 mm | MTL, high resistance builds |
| 34 AWG | 0.160 mm | MTL, high resistance builds |
Understanding Ohm's Law for Vaping
Ohm's Law is the foundation of all electrical calculations in vaping. Whether you're adjusting wattage on a regulated mod or building coils for a mechanical device, understanding these relationships keeps you safe and helps optimize your vape.
The Basic Formulas
The core relationship is: V = I × R
From this, we can derive:
- V (Voltage) = I × R
- I (Current/Amps) = V / R
- R (Resistance/Ohms) = V / I
- P (Power/Watts) = V × I = I²R = V²/R
Our calculator handles all these relationships automatically. Lock any two known values, and it solves for the rest.
Why This Matters for Vapers
When you press your fire button, your battery delivers voltage to your coil. The coil's resistance determines how much current flows. Too much current can exceed your battery's safe limits, potentially causing dangerous failures.
Regulated mods handle these calculations internally and protect against unsafe conditions. Mechanical mods provide no protection - you're responsible for ensuring your build is safe.
Building Safe Coils
Choosing Wire Material
Each wire type has distinct characteristics:
Kanthal A1 - The most popular choice for beginners. High resistance makes it forgiving, and it works only in wattage mode. Can be dry-burned for cleaning.
Nichrome N80 - Lower resistance than Kanthal, meaning faster ramp-up times. Slightly faster heating creates a more responsive vape. Wattage mode only.
Stainless Steel 316L - Versatile wire that works in both wattage and temperature control modes. Clean flavor profile. Can be dry-burned carefully.
Nickel (Ni200) - Extremely low resistance, designed exclusively for temperature control. Never use in wattage mode - this is dangerous. Cannot be dry-burned.
Titanium - Another TC-only wire with slightly higher resistance than nickel. Releases toxic oxides at high temperatures, so never dry burn. TC mode only.
Selecting Wire Gauge
Wire gauge is measured in AWG (American Wire Gauge). Lower numbers mean thicker wire:
- 20-22 AWG: Thick wire, low resistance. Needs higher power, longer ramp-up. Good for high-wattage cloud builds.
- 24 AWG: Popular all-around gauge. Balances heat capacity with ramp-up time.
- 26 AWG: Good for medium-wattage builds. Heats faster than thicker wire.
- 28-32 AWG: Thin wire, higher resistance. Perfect for MTL builds and restricted setups.
Thicker wire holds more heat and provides a warmer vape but takes longer to heat up. Thinner wire heats instantly but cools quickly too.
Coil Geometry
Inner Diameter (ID): The size of your wrapping rod determines coil ID. Common sizes are 2.5mm and 3mm. Larger IDs increase surface area but require more power.
Number of Wraps: More wraps mean higher resistance and more surface area. Fewer wraps mean lower resistance and faster heating. 5-7 wraps is typical for most builds.
Leg Length: Longer legs add resistance. Keep legs as short as practical to minimize wasted resistance.
Battery Safety
Battery safety is critical, especially for mechanical mod users. Even regulated mod users should understand these concepts.
Understanding CDR (Continuous Discharge Rating)
Your battery's CDR tells you the maximum continuous current it can safely deliver. This rating is in amps (A).
Common ratings from reputable cells:
- Sony VTC5A: 25A
- Samsung 25R: 20A
- LG HG2: 20A
- Molicel P26A: 25A
Always verify CDR from independent testers like Mooch - manufacturer claims are often exaggerated.
Calculating Amp Draw
For regulated mods, amp draw is calculated from the battery side, not the coil:
Amp Draw = Wattage / (Cutoff Voltage × Battery Count × Efficiency)
Most regulated mods cut off around 3.2V and operate at roughly 90% efficiency.
For mechanical mods, it's simpler (and more dangerous):
Amp Draw = Battery Voltage / Coil Resistance
A fully charged battery at 4.2V with a 0.2Ω coil draws 21A. If your battery is only rated for 20A, this is unsafe.
Building in a Safety Margin
Never run at 100% of your CDR. Aim for 80% maximum to account for:
- Cell degradation over time
- Voltage sag under load
- Real-world conditions differing from lab tests
Our Battery Safety calculator shows your headroom percentage. Keep this above 20% for comfortable margins.
Common Builds
MTL (Mouth-to-Lung) Builds
- Resistance: 0.8Ω - 1.5Ω
- Wire: 28-32 AWG Kanthal or SS316L
- Wraps: 5-8 on 2.5mm ID
- Power: 10-20W
RDL (Restricted Direct Lung) Builds
- Resistance: 0.4Ω - 0.8Ω
- Wire: 24-26 AWG Kanthal or SS316L
- Wraps: 5-7 on 3mm ID
- Power: 30-50W
DTL (Direct-to-Lung) Builds
- Resistance: 0.15Ω - 0.4Ω
- Wire: 22-24 AWG Kanthal or SS316L
- Wraps: 4-6 on 3mm ID
- Power: 50-100W
Cloud Chasing Builds
- Resistance: 0.1Ω - 0.2Ω
- Wire: 20-22 AWG Kanthal or SS316L
- Configuration: Dual or more coils
- Power: 100W+
- Requires high-drain batteries and appropriate mod
Safety Reminders
- Always check resistance with an ohm meter before installing a new build
- Never exceed your battery's CDR - this is non-negotiable
- Use regulated mods until you fully understand electrical safety
- Buy batteries from reputable vendors - counterfeit cells are dangerous
- Inspect wraps - rewrap damaged batteries immediately
- Don't mix batteries - use married pairs of the same brand, model, and age
- Store batteries safely in cases, never loose in pockets with keys or coins
This calculator provides estimates based on theoretical calculations. Always verify resistance with a physical ohm meter before use, and start at lower wattages when testing new builds.
Frequently Asked Questions
What is Ohm's Law and why is it important for vaping?
Ohm's Law describes the relationship between voltage (V), current (I), and resistance (R). The formula V = I × R is essential for vaping because it determines how much power your coil produces and how much current your batteries need to supply. Understanding this helps you build safe coils and choose appropriate wattage settings.
How do I calculate coil resistance?
Coil resistance depends on wire material, gauge (thickness), number of wraps, coil diameter, and leg length. Use our Coil Builder tab to input these values and get an accurate resistance calculation. The formula involves the wire's resistivity multiplied by length, divided by cross-sectional area.
What is a safe resistance for my coil?
Safe resistance depends on your batteries and mod type. For regulated mods, most accept 0.1Ω and above. For mechanical mods, never build below what your battery can safely handle. Use our Battery Safety tab to verify your specific setup. A common safe range for beginners is 0.5Ω to 1.5Ω.
What does CDR mean for vape batteries?
CDR stands for Continuous Discharge Rating, measured in amps. It's the maximum current your battery can safely deliver continuously without overheating or venting. Never exceed your battery's CDR. Common ratings are 15A, 20A, 25A, and 30A. Always buy batteries from reputable sources and verify their actual CDR ratings.
Why does wire material affect resistance?
Different metals have different resistivity values. Kanthal A1 has high resistivity, making it easy to achieve higher resistance. Stainless steel 316L has lower resistivity and works with temperature control. Nickel and titanium have very low resistivity and must only be used in TC mode - never in wattage mode.
What AWG wire gauge should I use?
Common gauges for vaping are 22-28 AWG. Lower numbers (22-24 AWG) are thicker, produce lower resistance, and handle higher power. Higher numbers (26-28 AWG) are thinner, produce higher resistance, and work better for MTL builds. 24-26 AWG is versatile for most applications.
How do I calculate recommended wattage for my coil?
Recommended wattage depends on coil surface area and desired heat flux. Our calculator estimates this based on your wire specifications. Generally, start low (around 75% of the ideal wattage shown) and increase until you find your preferred warmth and vapor production.
What's the difference between single and dual coils?
Dual coils are wired in parallel, halving the total resistance compared to a single coil. They produce more vapor and flavor but consume more battery and e-liquid. Single coils are more efficient and easier to build. Choose based on your device and preferences.
Why do mechanical mods require extra safety knowledge?
Mechanical mods have no electronic protection - they deliver raw battery power to your coil. If your coil shorts or resistance is too low, there's nothing to prevent battery overcurrent, which can cause venting or worse. Always calculate amp draw, use high-CDR batteries, and build within safe limits.
How do parallel battery configurations affect safety?
Parallel batteries effectively double (or triple) your CDR capacity, allowing higher wattage while staying safe. Two 20A batteries in parallel give you 40A capacity. Series batteries double voltage instead, which is used in some high-wattage regulated mods. Always use matched batteries from the same batch.