Volts, Amps, Ohms & Watts: The Electricity Behind Your Vape

• June 07 2026, by Steffen Adria
• 19 min reading time

Battery voltage and coil resistance set the maximum power your vape can make. What you actually get is decided by a circuit board that holds your wattage steady as the battery drains. Here's what amps, volts, ohms and watts each mean, with Ohm's law ceiling tables for one and two cells.

Your vape does not connect the battery straight to the coil. In almost every device made today there is a small circuit board in between, and its whole job is to decide how much power the coil gets, and to keep delivering that same power as the battery runs down. Volts, amps, ohms and watts are how that job is described.

Ohm's law still applies, and it still sets the limits. What it no longer does is set your wattage. On a mechanical mod, and roughly on a cheap disposable, the battery voltage and the coil resistance decide the power between them. On a pod kit or a box mod they only decide the ceiling, and you set the wattage underneath it, while the electronics work backwards to find the voltage and current needed. Here is what each unit means, and what your device is really doing with them.

What's an amp?

The amp (short for "ampere"), symbol "A", is the standard unit for electrical current. It is a measure of how much charge is passing a point in the circuit each second.

An amp-hour is a measure of battery capacity. It is usually quoted in milliamp-hours (a milliamp being 1/1000th of an amp), a milliamp-hour being the capacity to deliver one milliamp for one hour.

For example, the EFEST 18650 3500 mAh battery has a capacity of 3500 mAh. It might seem like that should mean 3.5 amps for an hour, but cells deliver less usable capacity at high current, so real-world runtime is shorter than the rating suggests.

Capacity is not the same as current capability, and the two trade off against each other. Every cell also has a continuous discharge rating (CDR), which is the current it can supply safely and continuously. On high-capacity 18650s that figure is often around 10 A, well below what the headline capacity might lead you to expect. The CDR, not the capacity, is the number that decides whether a cell is safe in a given device.

What's a volt?

The volt, symbol "V", is the standard unit for electrical potential, or the driving force of a circuit. More voltage across a given resistance means more current.

Lithium-ion cells are the voltage source in a vape. A single cell is rated at about 3.7 V, but that is a nominal average, not a constant. A full cell sits at 4.2 V and is considered empty at about 3.2 V, sliding down through that range as it discharges, and sagging further under heavy load. That slide is the problem the circuit board exists to solve.

What's an ohm?

The ohm, symbol "Ω", is the standard unit for electrical resistance. It sets how much current flows for a given voltage.

In vaping, resistance is a property of the coil. It is determined by the wire's thickness (thicker is less resistive), its length (longer is more resistive), and its material. Coils are typically made from FeCrAl, an alloy of iron, chromium and aluminium sold under brand names like Kanthal. It is the usual choice because it stands up to being heated and cooled thousands of times without corroding. Stainless steel and nichrome are the other two common materials, and the heating element itself is now more often a mesh strip than a wound wire. Most coils sit between about 0.15 and 1.4 ohms.

What is a sub-ohm device?

A sub-ohm device is a coil, tank or device with a resistance below 1.0 ohms. Low-resistance coils are built for high-power, high-airflow, direct-to-lung vaping and produce a lot of vapour, which is why they are paired with freebase e-liquid rather than salt nicotine. As the tables below show, low resistance is what raises the ceiling. It is the only way to get a lot of power out of a coil at a voltage a lithium cell can actually produce.

What's a watt?

A watt, symbol "W", is a unit of power, meaning energy delivered per unit time. A more familiar unit for some readers is the horsepower, equal to 746 W. Power is what actually vaporizes e-liquid: more watts into the coil means more heat, faster, and more vapour.

How are these units related?

Volts, ohms and amps are tied together by Ohm's law: current equals voltage divided by resistance.

V = I × R, where V is voltage, I is current and R is resistance.

Power follows from it, in three equivalent forms:

P = V × I    P = V² / R    P = I² × R

These are always true. What changes from device to device is which of these quantities is fixed and which one is the result, and that is decided by the electronics.

The ceiling: the most power a coil can take

Start with what the battery makes possible. Whatever the electronics do, they cannot push more power into a coil than the available voltage allows:

P_max = V_max² / R

The tables below give that ceiling for the two common battery arrangements, at nominal voltage and at full charge. Read them as limits, not settings. No regulated device delivers these figures, and most cap out well below them.

One cell (3.7 V nominal, 4.2 V full)

Resistance (Ω)	Maximum current at 4.2 V (A)	Maximum power at 4.2 V (W)	Maximum power at 3.7 V (W)
0.15	28.0	117.6	91.3
0.2	21.0	88.2	68.5
0.4	10.5	44.1	34.2
0.6	7.0	29.4	22.8
0.8	5.2	22.1	17.1
1.0	4.2	17.6	13.7
1.2	3.5	14.7	11.4
1.4	3.0	12.6	9.8

The gap between the two power columns is the whole reason regulation exists. A 1.2-ohm coil wired straight to a cell makes 14.7 W when the cell is full and 8.5 W by the time it reaches 3.2 V, a 42% fade, and that percentage is the same at every resistance. It is exactly what people describe when a disposable "dies slowly." It is not a fault; it is arithmetic.

Two cells in series (7.4 V nominal, 8.4 V full)

Resistance (Ω)	Maximum current at 8.4 V (A)	Maximum power at 8.4 V (W)	Maximum power at 7.4 V (W)
0.15	56.0	470.4	365.1
0.2	42.0	352.8	273.8
0.4	21.0	176.4	136.9
0.6	14.0	117.6	91.3
0.8	10.5	88.2	68.5
1.0	8.4	70.6	54.8
1.2	7.0	58.8	45.6
1.4	6.0	50.4	39.1

Take this table seriously as a warning rather than a target. Those top rows are theoretical figures for an unregulated series mod, and the current column is the reason: 42 A drawn through both cells, when a good 18650 is rated for 20 to 30 A continuous and a high-capacity one for around 10. No regulated dual-cell mod produces these numbers; a 200 W mod is 200 W because its converter stops there. What a second cell actually buys you is not a higher ceiling at the coil but a higher supply voltage, which lets the converter deliver the same wattage while drawing roughly half the current from each cell.

What actually sits between your battery and your coil

Unregulated: the coil sees the raw battery

In a mechanical mod, and in most inexpensive draw-activated disposables, the switch simply connects the cell to the coil. The coil gets whatever the battery happens to be at, so the device runs at the ceiling and falls with it. Teardowns of common disposable controllers find no converter at all, just a MOSFET, a current limit, an under-voltage cut-off around 3.25 V and a maximum puff timer.

Regulated: a converter and a microcontroller

Every pod kit and box mod worth the name adds three things: a microcontroller, a power MOSFET to switch the coil, and a way of controlling the voltage that reaches it. The controller measures the coil's resistance, takes the wattage you have set (or the wattage the device was built for), and works out the voltage it needs to produce:

V = √(P × R)    and    I = √(P / R)

Then it produces that voltage and holds it there, adjusting continuously as the cell sags. Three techniques do the actual work:

• PWM (duty-cycle switching). The cheapest approach: the MOSFET switches the coil on and off very rapidly, and the coil's thermal mass averages the result. On half the time at 4.2 V delivers roughly half the power. It can only ever bring power down from the ceiling, never above it, but for a fixed-wattage pod that is usually all that is needed.
• Buck (step-down) converter. An inductor-based switching circuit that turns a higher input voltage into a genuinely lower output voltage, at a higher current, with very little waste. This is what multi-cell mods use, and what any device does whenever the coil needs less voltage than the cell currently sits at.
• Boost (step-up) converter. The same idea in reverse: it produces an output higher than the cell feeding it. This is the only way to get above the single-cell ceiling. To run a 1.2-ohm coil at 20 W, for instance, the board has to boost, because the table above caps a bare 4.2 V cell at 14.7 W.

These conversions are efficient, but not free. Real vape converters run somewhere around 85% to 97%, with the losses coming out of your battery as heat. Evolv publishes 85% for its single-cell DNA 60 and DNA 75 modules and 97% for the three-cell DNA 250.

You can often read the topology straight off a spec sheet by comparing the output voltage range with the input. The DNA 75 takes 3.0–4.2 V from one cell and puts out up to 6.2 V, which is above anything its cell can supply, so it boosts. The DNA 250 runs on a three-cell pack at 9.0–12.6 V and tops out at 9.3 V, below the pack voltage it works from, so it steps down.

So why do fixed-wattage devices exist?

A device like the Vaporesso XROS 3 Nano has no wattage buttons at all; it runs at 11 W or 16 W, and its chip selects between them according to which pod is fitted. That is not the absence of regulation. It is regulation with the target set at the factory instead of by you. The pods are 0.6 and 0.8 ohms, so the board needs to produce about 3.10 V for 16 W into the 0.6-ohm pod, or about 2.97 V for 11 W into the 0.8-ohm one, and it holds that figure from a full cell down to an empty one. Without the board, that same 0.8-ohm pod would start at 22.1 W and finish at 12.8 W.

What your device is actually producing

Below the ceiling, wattage is the input and voltage and current are the outputs. The table shows what the board is doing at a wattage typical for each coil:

Coil (Ω)	Typical setting (W)	Voltage the device produces (V)	Current through the coil (A)
1.2	12	3.79	3.16
1.0	13	3.61	3.61
0.8	16	3.58	4.47
0.6	22	3.63	6.06
0.4	40	4.00	10.00
0.2	60	3.46	17.32
0.15	80	3.46	23.09

Notice how narrow the voltage column is. From a 12 W mouth-to-lung pod to an 80 W mesh coil, the working voltage stays in a band of roughly 3 to 4.5 V, while the current ranges from about 3 A to over 23 A. That is not a coincidence: coils are designed backwards from what a lithium cell can comfortably supply, and everything else is done with current.

Hold the wattage constant instead and the picture inverts:

Coil (Ω)	Set power (W)	Voltage required (V)	Coil current (A)
0.2	25	2.24	11.18
0.4	25	3.16	7.91
0.6	25	3.87	6.45
0.8	25	4.47	5.59
1.0	25	5.00	5.00
1.2	25	5.48	4.56

Same 25 W all the way down, but the voltage more than doubles while the current is cut by more than half. Watch where the voltage crosses 4.2 V: above about 0.7 ohms, 25 W is out of reach for a single cell even at full charge, and that limit tightens to roughly 0.55 ohms once the cell has sagged to 3.7 V. Past those points a boost converter is not a refinement, it is a requirement.

Why your mod won't hit its rated wattage

The ceiling in practice is usually not the battery but the converter, because most devices publish a maximum output voltage lower than the pack can supply. The SMOK IPX 80 is a clean example: single cell, 1–80 W, resistance range 0.15–3.0 ohms, and an output range of 0.5–4.0 V. Put those together with P_max = V_max² / R and the 80 W on the box is only available on coils of about 0.2 ohms or lower. Fit a 0.4-ohm coil and the ceiling is 40 W; a 0.8-ohm coil caps out at 20 W; a 1.2-ohm coil at 13 W.

Nothing is broken when this happens. The coil is simply asking for a voltage the converter is not built to make. It is also why devices publish a supported resistance range alongside a maximum wattage. The two numbers are not independent, and neither is a promise on its own.

The amps that matter for battery safety

Here is the most important practical consequence of regulation, and the one most often got wrong: on a regulated device, the current through the coil is not the current coming out of the battery.

The converter transforms voltage, so it transforms current too. What the battery actually supplies is set by power, cell voltage and efficiency:

I_battery ≈ P / (efficiency × V_cell)

The gap can be large in either direction. Evolv rates the three-cell DNA 250 to deliver up to 55 A to the coil while drawing 28 A from the pack, which is a step-down. On a boosting single-cell board the relationship runs the other way, and the cell supplies more current than the coil ever sees.

Two things follow. First, at a fixed wattage the battery current rises as the cell drains, because the same power has to come out of a lower voltage, so the hardest moment for your battery is when it is nearly empty, not when it is full. Second, this is the number to check a cell's continuous discharge rating against. At 90% efficiency, a single-cell device draws roughly:

Set power (W)	Battery current at 3.7 V (A)	Battery current at 3.3 V (A)
11	3.3	3.7
16	4.8	5.4
25	7.5	8.4
40	12.0	13.5
60	18.0	20.2
80	24.0	26.9

A high-capacity 18650 with a 10 A continuous rating is therefore comfortable to roughly 30 W in a single-cell regulated mod, and no higher, regardless of which coil is fitted. Always take the CDR from the manufacturer's own figures rather than the headline capacity, keep wraps undamaged, and never carry loose cells with keys or coins.

What this means for choosing a device

Coil resistance still matters, and Ohm's law still governs it, but it sets your limits rather than your settings. A lower resistance raises the ceiling and lets a device reach high wattages at a voltage a lithium cell can realistically produce. Under that ceiling, the electronics deliver whatever power you asked for.

Practically:

• Higher-resistance coils (0.8–1.4 Ω) suit mouth-to-lung vaping at 10–20 W, run cooler, use less liquid and are paired with salt nicotine.
• Sub-ohm coils (0.15–0.6 Ω) suit direct-to-lung vaping at 25–80 W and above, produce far more vapour, and go through both liquid and battery much faster.
• Fixed-wattage pods and closed systems have made the choice for you, and the coil in the pod is matched to it.
• A disposable's output really does fade, by around 42% across its life, because there is usually nothing in there holding it steady.

The one thing that has not changed: a 200 W mod is still pushing more than a quarter of a horsepower through a piece of wire the size of a grain of rice. It just takes rather more electronics to do it than a battery and a coil.

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