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Convert battery capacity from milliamp-hours (mAh) to watt-hours (Wh). Check if your power bank meets airline carry-on regulations.
Most power banks use 3.7V (single Li-ion cell nominal voltage)
Where Wh is energy in watt-hours, mAh is capacity in milliamp-hours, and V is voltage in volts.
A 20,000 mAh power bank at 3.7V:
Wh = (20,000 × 3.7) ÷ 1000 = 74 Wh
| Capacity (mAh) | Energy (Wh) | Airline Status |
|---|---|---|
| 2,000 mAh | 7.4 Wh | ✓ Allowed |
| 3,000 mAh | 11.1 Wh | ✓ Allowed |
| 5,000 mAh | 18.5 Wh | ✓ Allowed |
| 10,000 mAh | 37.0 Wh | ✓ Allowed |
| 15,000 mAh | 55.5 Wh | ✓ Allowed |
| 20,000 mAh | 74.0 Wh | ✓ Allowed |
| 26,800 mAh | 99.2 Wh | ✓ Allowed |
| 27,000 mAh | 99.9 Wh | ✓ Allowed |
| 30,000 mAh | 111.0 Wh | ⚠ Approval needed |
| 50,000 mAh | 185.0 Wh | ✗ Prohibited |
| Device | mAh | Wh |
|---|---|---|
| iPhone 15 Pro Max | 4,422 | 16.4 |
| Samsung Galaxy S24 Ultra | 5,000 | 18.5 |
| iPad Pro 12.9" | 10,758 | 39.8 |
| MacBook Air M2 | ~14,000 | 52.6 |
| MacBook Pro 14" | ~19,000 | 70 |
| Anker 737 Power Bank | 24,000 | 88.8 |
| Maximum Carry-on Limit | ~27,000 | 100 |
The mAh to Wh conversion translates battery capacity from milliamp-hours (a measure of electrical charge) to watt-hours (a measure of energy). While mAh tells you how much current a battery can deliver over time, it does not account for voltage, making it unreliable for comparing batteries at different voltages. Watt-hours provide a universal energy measurement by incorporating voltage: Wh = (mAh × V) ÷ 1,000. This conversion is critically important for airline travel compliance, as the FAA, IATA, and most international aviation authorities regulate lithium batteries by watt-hours, not milliamp-hours. Batteries under 100 Wh may be carried on without restriction, those between 100–160 Wh require airline approval, and those exceeding 160 Wh are prohibited on passenger aircraft. The standard lithium-ion cell voltage of 3.7V means a 27,027 mAh battery hits the 100 Wh threshold, making this conversion essential for frequent travelers and electronics enthusiasts.
Check the battery label, product specifications, or manufacturer website for the mAh capacity. Power banks typically display this prominently (e.g., 10,000 mAh, 20,000 mAh). For phones, check Settings > Battery or the device spec sheet.
Use the nominal cell voltage, not the charging or output voltage. Standard lithium-ion/polymer: 3.7V. LiFePO4: 3.2V. For multi-cell packs, use the total pack voltage (e.g., 2-cell = 7.4V, 3-cell = 11.1V).
Multiply mAh by the voltage, then divide by 1,000. Example: 20,000 mAh at 3.7V = (20,000 × 3.7) ÷ 1,000 = 74 Wh. This battery is safe for airline carry-on.
Compare your Wh result against FAA/IATA limits: under 100 Wh is unrestricted carry-on, 100–160 Wh needs airline approval (max 2 per passenger), and over 160 Wh is prohibited. All lithium batteries must be in carry-on, never checked luggage.
FAA and IATA regulations limit carry-on lithium batteries to 100 Wh (or 160 Wh with approval). Knowing your battery's Wh rating prevents confiscation at airport security checkpoints.
mAh is meaningless for comparing batteries at different voltages. Converting to Wh provides a true apples-to-apples energy comparison across all battery chemistries and configurations.
Knowing the Wh capacity lets you accurately estimate how long a power bank can charge your devices, accounting for voltage conversion losses between the battery and USB output.
| mAh | 3.2V (LiFePO4) | 3.7V (Li-ion) | 7.4V (2-cell) | 11.1V (3-cell) |
|---|---|---|---|---|
| 3,000 mAh | 9.6 Wh | 11.1 Wh | 22.2 Wh | 33.3 Wh |
| 5,000 mAh | 16.0 Wh | 18.5 Wh | 37.0 Wh | 55.5 Wh |
| 10,000 mAh | 32.0 Wh | 37.0 Wh | 74.0 Wh | 111.0 Wh |
| 20,000 mAh | 64.0 Wh | 74.0 Wh | 148.0 Wh | 222.0 Wh |
| 27,027 mAh | 86.5 Wh | 100.0 Wh | 200.0 Wh | 300.0 Wh |
| 30,000 mAh | 96.0 Wh | 111.0 Wh | 222.0 Wh | 333.0 Wh |
At the standard lithium-ion voltage of 3.7V: 20,000 × 3.7 ÷ 1,000 = 74 Wh. This is comfortably under the 100 Wh FAA/IATA airline carry-on limit. However, if the battery uses a 2-cell (7.4V) configuration with 20,000 mAh, it would be 148 Wh, requiring airline approval.
For standard 3.7V lithium-ion batteries, the 100 Wh limit translates to approximately 27,027 mAh. A 26,800 mAh or 27,000 mAh power bank is the largest common size that stays under the limit without special approval. Always verify the Wh rating printed on the battery label, as some manufacturers rate capacity differently.
mAh produces larger, more impressive-sounding numbers that are more marketable. A 20,000 mAh power bank sounds much more substantial than a 74 Wh one. Additionally, consumers are accustomed to seeing mAh on phone battery specs. However, Wh is the technically correct unit for comparing energy storage capacity across different devices and voltages.
Convert both batteries to Wh, then divide the power bank Wh by the phone battery Wh and multiply by 0.80–0.90 for conversion efficiency losses. Example: 74 Wh power bank charging a 16.4 Wh iPhone 15 Pro Max = 74 ÷ 16.4 × 0.85 = approximately 3.8 full charges.
Always use the nominal cell voltage (3.7V for Li-ion/LiPo, 3.2V for LiFePO4), not the USB output voltage (5V). The mAh rating on most power banks and phones refers to the internal cell capacity at its nominal voltage. If the device already lists a Wh rating on its label, use that official value for airline compliance rather than calculating from mAh.