mAh to Wh Converter — Free Online Calculator
Convert milliamp-hours (mAh) to watt-hours (Wh) for battery capacity comparison. Works for phone, laptop, and power bank batteries.
How to Use This Calculator
Enter battery capacity in mAh and select the voltage.
The Formula Explained
Wh = mAh × V / 1000. This is the actual energy stored in the battery. Airlines limit batteries to 100 Wh (carry-on) or 160 Wh (with approval).
mAh vs Wh: Understanding Battery Capacity
Battery capacity ratings on consumer products often confuse buyers because two completely different units are used. Phone batteries are rated in mAh (milliamp-hours), while laptops, power banks for electronics, and electric vehicle batteries are usually rated in Wh (watt-hours) or kWh. The two units measure related but different things: mAh measures charge capacity at a specific voltage, while Wh measures energy regardless of voltage. Converting between them requires knowing the battery voltage.
The formula is simple: Wh = (mAh × V) / 1000. A typical smartphone battery with 4,000 mAh at 3.85V = 15.4 Wh. A laptop battery with 60 Wh at 11.1V = 60,000 / 11.1 = 5,405 mAh (though laptop specs almost always use Wh directly). The confusion arises because consumer marketing favors mAh for small batteries (bigger number) and Wh for larger batteries. When comparing capacity across devices with different voltages, always convert to Wh first.
Worked Example: Power Bank Capacity
A "20,000 mAh" power bank from a reputable brand. Internal voltage: 3.7V (lithium-ion cells). Theoretical energy: 20,000 × 3.7 / 1000 = 74 Wh. This is the actual stored energy, which is what matters for real-world use.
Output via USB-A (5V): boost converter converts from 3.7V to 5V with about 90% efficiency. Usable output at 5V: 74 × 0.90 = 66.6 Wh at 5V equivalent, or 66,600 / 5 × 1000 = 13,320 mAh at 5V.
Charging a 4,000 mAh phone (3.85V internal, 5V USB input): each charge requires about 4,000 × 5 / 3.85 / 0.88 (phone charging efficiency) = 5,904 mAh of power bank output at 5V. Real-world recharges: 13,320 / 5,904 = 2.25 full charges, matching typical observed performance.
This is why "20,000 mAh" power banks rarely deliver 5 full phone charges despite phones being rated 3,000-4,000 mAh. The marketing number is accurate for the internal 3.7V battery, but real-world USB output is lower due to voltage conversion and losses.
Worked Example: Airline Battery Limits
Traveling with multiple devices: iPhone (12 Wh / 3,250 mAh), iPad (37 Wh / 10,000 mAh), MacBook (84 Wh), 20,000 mAh power bank (74 Wh), Kindle (6 Wh). Total: 213 Wh in devices, 74 Wh in the power bank.
FAA rules: devices are fine (installed in the device). Power bank 74 Wh is well under the 100 Wh limit — no airline approval needed. If the power bank were a 40,000 mAh unit at 3.7V = 148 Wh, airline approval would be required (between 100-160 Wh). At 50,000 mAh / 185 Wh, prohibited on passenger aircraft.
Large camera batteries, laptop spares, and power stations commonly exceed 100 Wh. Always check the Wh rating printed on the battery (required by most manufacturers for aviation compliance) before packing for a flight. Lithium batteries must be in carry-on only, never checked baggage.
Five mAh/Wh Conversion Mistakes
1. Forgetting to include voltage. You cannot convert mAh to Wh without knowing the voltage. Different batteries at different voltages have different Wh for the same mAh.
2. Using nominal vs actual voltage. A lithium-ion cell nominal voltage is 3.7V but actual voltage varies from 4.2V (full) to 3.0V (empty). Wh calculations use nominal voltage.
3. Assuming 100% efficiency through converters. USB power delivery, wireless charging, and DC-DC converters all have losses (5-15% typically). Usable output is less than stored energy.
4. Comparing mAh across different voltages. A 3,000 mAh phone battery (3.7V = 11.1 Wh) has less energy than a 2,000 mAh camera battery at 7.4V (14.8 Wh). Always compare Wh.
5. Ignoring calendar aging. Lithium batteries lose 2-3% capacity per year even when unused. A 5-year-old 10,000 mAh battery is really about 8,500 mAh. Cycle aging adds further losses.
Common Battery Capacities
Smartphone: 3,000-5,000 mAh at 3.7V = 11-18 Wh.
Smartwatch: 250-600 mAh = 0.9-2.2 Wh.
Wireless earbuds (total case): 400-600 mAh = 1.5-2.2 Wh.
Tablet: 6,000-10,000 mAh at 3.7V = 22-37 Wh.
Laptop: 40-100 Wh (typically rated directly in Wh).
Small power bank: 5,000-10,000 mAh = 18-37 Wh.
Large power bank: 20,000-30,000 mAh = 74-111 Wh.
Portable power station: 150-2,000 Wh (e.g., Jackery, EcoFlow, Goal Zero).
E-bike battery: 300-750 Wh typical.
Electric scooter: 250-1,000 Wh.
Electric car: 40-100+ kWh (40,000-100,000+ Wh).
Standards and Regulations
UN 38.3 is the international test standard for lithium battery transportation. Every lithium battery shipped internationally must pass UN 38.3 testing for vibration, shock, temperature, altitude, and short circuit. IEC 62133 covers safety of portable sealed batteries. FAA/TSA rules for carry-on lithium batteries: under 100 Wh no approval, 100-160 Wh with airline approval, over 160 Wh prohibited. UN 3480/3481 are the dangerous goods classification codes for lithium-ion batteries and batteries contained in equipment.
mAh to Wh: battery capacity in two different units
Battery capacity gets listed two ways. Phones and small electronics use milliamp-hours (mAh) because the math is simpler at low voltages. Laptops, power tools, and EVs use watt-hours (Wh) because that scales meaningfully across systems with different voltages. Converting between the two requires the nominal cell or pack voltage.
The formula and what it does
A 5000 mAh phone battery at nominal 3.7 V (single Li-ion cell) holds 5000 x 3.7 / 1000 = 18.5 Wh. A 50 Wh laptop pack at 11.1 V (3 cells in series) is 50 / 11.1 x 1000 = 4500 mAh of pack capacity. These conversions are exact at the nominal voltage; real energy depends on discharge rate and temperature.
Worked example
Scenario: Compare a 10,000 mAh USB power bank and a 26,800 mAh laptop power bank.
The USB pack at 3.7 V: 10,000 x 3.7 / 1000 = 37 Wh. The laptop pack at typically 14.8 V (4S): 26,800 x 14.8 / 1000 = 396 Wh. So the laptop pack holds 10.7x the energy, not 2.68x as the mAh numbers alone suggest. This is why airline carry-on limits (100 Wh for unrestricted, 160 Wh with airline approval) are stated in Wh, not mAh.
Common mistakes to avoid
undefinedFrequently asked questions
Why does the FAA use Wh and not mAh for battery limits?
Because mAh comparisons across voltages are misleading. 100 Wh is the actual fire-risk threshold, and it requires knowing both mAh and V. The Wh number is the safety-meaningful one.
What voltage should I use for Li-ion?
Nominal voltage is 3.7 V per cell. Fully charged is 4.2 V; cutoff is 3.0 V. Use 3.7 V for energy calculations. For LiFePO4, use 3.2 V nominal.
Does discharge rate affect actual capacity?
Yes. Battery capacity is rated at a slow discharge (typically C/20 for lead-acid, 0.5C for Li-ion). At higher current, you get less capacity. This is called Peukert effect for lead-acid; smaller effect on lithium chemistries.
Why does my phone battery say 4400 mAh but the actual runtime suggests less?
Two reasons: marketing rating vs usable capacity (cutoff voltage), and power consumption varies with screen brightness, signal, app load. Real-world usage is usually 60-80 percent of nameplate Wh.
How big is an EV battery in mAh terms?
A 75 kWh Tesla pack at 350 V nominal: 75,000 / 350 x 1000 = 214,286 mAh. Useless metric at that scale, which is why EV packs are always Wh or kWh.
How do I calculate runtime?
Wh divided by load wattage. A 100 Wh battery powering a 25 W load runs about 4 hours, minus losses (typical efficiency 85-92 percent for Li-ion).