mAh to Ah Calculator
Take a milliamp-hour figure off a phone, power bank, drone pack or cell and put it on the same footing as the amp-hour specs that larger batteries are sold with.
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mAh to Ah Calculator
Updates as you type- Entered, in mAh
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- Energy at that voltageWh = Ah × V. The only figure that compares across battery types
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Ah = mAh ÷ 1,000 · Wh = Ah × V
How this is calculated
An amp-hour is a quantity of electric charge: one amp flowing for one hour. A milliamp-hour is a thousandth of that, and the conversion between them is the SI prefix and nothing else — the same relationship as metres to millimetres, exact and unconditional.
Which leaves the interesting question, because the arithmetic is not it. Why does a phone advertise 4,000 mAh while a car battery advertises 60 Ah, when those are the same kind of measurement?
Nobody standardised it. Each category drifted toward whichever unit produced a number that reads well: a phone in amp-hours is "4", a car battery in milliamp-hours is "60,000", and both are worse than what they settled on. In consumer electronics there is a commercial pull in the same direction, since a larger figure looks like a larger battery on a spec sheet where nobody reads the unit. The result is a genuine hazard — two specifications describing the identical physical quantity, differing by a factor of a thousand, with nothing on either label to flag it.
There is a second, subtler problem with taking any capacity figure at face value.Capacity is quoted under test conditions, not guaranteed under yours. An alkaline AA rated 2,500 mAh will deliver that into a slow drain like a clock and well under half of it into a camera flash, because internal resistance wastes more of the charge as heat the harder you pull. Cold makes it worse again. Two mAh figures measured under different conditions are not strictly comparable even in the same unit.
And the figure that actually matters for most questions is not capacity at all. Amp-hours measure charge; energy is charge times voltage. That is why a 5,000 mAh drone pack at 11.1 V holds roughly three times the energy of a 5,000 mAh phone battery at 3.85 V, despite the identical headline number, and why any comparison that crosses a voltage boundary has to be made in watt-hours.
Worked example
One full calculation with real numbers, so you can follow along and check the tool by hand.
Two batteries most people own, both firmly inside "small electronics", and the distance between them is larger than the category suggests.
A 3,000 mAh phone battery. Divided by a thousand, that is3.0 Ah. At a nominal 3.85 V it holds 11.55 Wh — about enough to run a 10 W LED bulb for an hour.
A 20,000 mAh power bank. Same arithmetic, 20 Ah, and at its internal 3.7 V that is roughly 74 Wh. So within a single category, and within two things you might carry in the same bag, the capacity range spans nearly seven times over.
Which invites the obvious conclusion — 20 Ah divided by 3 Ah is 6.7, so the bank should charge the phone six or seven times. It will not. It will manage about four, and the gap is worth understanding because it is not a defect.
The bank's 20,000 mAh is measured at its internal cell voltage of 3.7 V, a place no user ever touches. Everything you plug in receives 5 V from the USB port instead, and converting up costs something. Charging the phone's own cell from that 5 V costs more again. Between 60% and 70% of the nameplate energy reaching the phone is entirely normal, which puts real usable output nearer13,000 mAh at 5 V, and four charges rather than six.
The lesson generalises past power banks. A capacity figure is only meaningful alongside the voltage it was measured at, and comparing two figures measured at different voltages produces a ratio that is arithmetically correct and practically wrong. Converting mAh to Ah gets the units aligned; converting to watt-hours is what gets the comparison honest.
Visual comparison
| Category | Bar | Typical capacity (mAh) | In amp-hours |
|---|---|---|---|
| AA alkaline cell | 2500 | = 2.5 Ah | |
| Smartphone | 4000 | = 4 Ah | |
| Laptop | 6000 | = 6 Ah | |
| USB power bank | 20000 | = 20 Ah | |
| Car starter battery | 60000 | = 60 Ah | |
| Deep-cycle or solar battery | 100000 | = 100 Ah |
Source: Category midpoints only. A specific model can sit well outside the range its category suggests.
Reference tables
The table exists to answer a question the converter cannot: not what your number becomes, but whether it is the number you thought you had. Find the category closest to your device and check the range — a figure well outside it usually means the spec was in the other unit, or that it describes something other than the cell you assumed.
The labelled in column is the one to read before making any comparison. It records the convention each category actually uses, and every place that column changes between two rows is a place where two spec sheets will differ by a thousand without saying so. The e-bike row is the boundary: it is the smallest thing normally sold in amp-hours, and a 14 Ah e-bike pack holds far more energy than a 20,000 mAh power bank despite the smaller-looking number.
The energy column is the one that compares fairly, and it reorders the list. By capacity a power bank beats a drone pack comfortably; by energy the drone pack wins, because it runs at three times the voltage. Any time you are weighing two batteries from different rows, that is the column to use.
Every range here is approximate and model-dependent. They are landmarks for establishing scale, not specifications — read the label on the actual battery for anything that matters.
| Category | Typical range | Labelled in | NominalV | Typical energyWh | Worth knowing |
|---|---|---|---|---|---|
| Wireless earbud case | 300 – 800 mAh | mAh | 3.7 | 1.9 | Often quoted for the case and the buds together, which are separate cells with separate capacities. |
| AA alkaline cell | 1,800 – 3,000 mAh | mAh | 1.5 | 3.8 | Alkaline capacity falls sharply at high discharge rates, so the printed figure holds only for a gentle load. |
| 18650 lithium cell | 2,000 – 3,500 mAh | mAh | 3.7 | 11.1 | The building block inside laptops, power banks and e-bike packs. Anything claiming much over 3,500 is not what it says. |
| Smartphone | 3,000 – 5,500 mAh | mAh | 3.85 | 15.4 | A single cell, so the mAh figure is directly comparable between handsets — one of the few places it is. |
| Drone or RC LiPo pack | 1,500 – 6,000 mAh | mAh | 11.1 | 33.3 | Cells in series, so the pack voltage is three or four times a phone’s and the energy far higher for the same mAh. |
| Laptop | 4,000 – 8,000 mAh | mAh | 11.4 | 68.4 | Increasingly labelled in Wh instead, because the pack voltage varies by model and mAh alone will not compare them. |
| USB power bank | 5,000 – 27,000 mAh | mAh | 3.7 | 74 | Rated at internal cell voltage. Usable charge out of the USB port at 5 V is roughly two thirds of the printed number. |
| E-bike battery | 10 – 20 Ah | Ah | 36 | 504 | The category where the labelling convention flips. A 14 Ah e-bike pack holds far more energy than a 20,000 mAh power bank. |
| Car starter battery | 45 – 75 Ah | Ah | 12 | 720 | Sold on cold cranking amps rather than capacity, because its job is a huge current for seconds, not a small one for hours. |
| Deep-cycle or solar battery | 50 – 300 Ah | Ah | 12 | 1200 | Built to be discharged deeply and repeatedly, which a starter battery is not. 100 Ah at 12 V is the reference size. |
Common mistakes
Comparing a raw mAh number against an Ah number
A "20,000" power bank looks like two hundred times a "100" car battery, and it is actually a fifth of it. The units are a thousand apart and neither label warns you. Convert both to the same unit before any comparison, every time — this is the single most common battery-spec error there is.
Adding up the cells in a series pack
A 3S drone pack built from three 2,200 mAh cells is a 2,200 mAh pack at 11.1 V, not a 6,600 mAh one. Stacking cells in series multiplies voltage and leaves capacity alone. The energy does triple — but it is the voltage that tripled, not the number on the label.
Believing a capacity claim that physics rules out
Marketplace listings for 18650 cells claiming 6,000 or 9,900 mAh are not optimistic, they are fabricated. The chemistry and the can size cap a genuine 18650 at roughly 3,500 mAh, so any figure meaningfully above that is a re-wrapped lower-capacity cell at best.
Assuming two mAh figures were measured the same way
Capacity is quoted at a particular discharge rate and temperature. An alkaline AA rated 2,500 mAh at a gentle drain can deliver under half that into a camera flash, and cold weather takes more again. The figure is a condition, not a constant.
Confusing a charger’s mA with a battery’s mAh
They differ by a unit of time and describe unrelated things. A 2,000 mA charger delivers two amps at any moment; a 2,000 mAh cell stores two amp-hours in total. The charger figure sets how fast the cell fills, and says nothing about how much it holds.
This tool provides planning estimates. Always verify final values against your local code and a licensed electrician.
Frequently asked questions
Why do phones use mAh when car batteries use Ah?
Readability, and nothing more principled than that. A phone battery in amp-hours is "4" and a car battery in milliamp-hours is "60,000" — each category settled on whichever unit gives a number that reads well at a glance. There is a commercial nudge too: in consumer electronics a bigger number sells better, and milliamp-hours produce a bigger number. The physics is identical either way; only the prefix moves.
Is a higher mAh always better?
Only when you are comparing like with like — the same battery chemistry at the same voltage in the same kind of device. A 5,000 mAh phone genuinely lasts longer than a 3,000 mAh phone with similar hardware. A 5,000 mAh drone pack and a 5,000 mAh phone battery hold very different amounts of energy, because the drone pack runs at three times the voltage. And higher capacity in the same physical size usually trades against cycle life or discharge rate, so the biggest number is not automatically the best cell.
How do I convert mAh to watt-hours?
Divide the mAh by 1,000 to get amp-hours, then multiply by the battery’s nominal voltage. A 3,000 mAh phone battery at 3.85 V is 3 × 3.85 = 11.55 Wh. Watt-hours are the figure that compares honestly between different battery types, and they are also what airlines regulate carry-on batteries by — the common 100 Wh limit is a watt-hour figure precisely because milliamp-hours would mean different things for different packs.
How many times will a 20,000 mAh power bank charge my phone?
About four, for a typical 3,000 mAh phone — not the six or seven the raw division suggests. The bank’s rating is measured at its internal 3.7 V, so it holds around 74 Wh. Stepping that up to 5 V for the USB port costs something, and charging the phone’s own cell costs more again. Between 60% and 70% of the nameplate actually reaching the phone is normal and not a sign of a bad product.
Does a battery keep its rated mAh over its life?
No. Lithium cells lose capacity with both cycles and age, typically retaining around 80% after a few hundred full cycles, and they degrade on the shelf even unused. The rating is a specification for a new cell under laboratory conditions. This is why a phone that once ran all day stops doing so long before it stops working, and why replacement capacity figures should be treated as a ceiling rather than a promise.
Is 1 Ah exactly 1,000 mAh?
Yes, exactly, with no rounding and no conditions attached. Milli- is the SI prefix for one thousandth, so the relationship is definitional in the same way that a kilometre is a thousand metres. Nothing about the battery, its chemistry, its age or its temperature changes it — those things change how many amp-hours the battery actually delivers, but not what an amp-hour is.