Power Bank Watt-Hour Calculator
Convert power bank mAh to watt-hours, calculate usable energy, and find out how many phone/tablet charges you can get.
Calculate Power Bank Energy
Enter your power bank's mAh rating and voltage to find real watt-hours.
How to Calculate Power Bank Watt-Hours from mAh (Wh Formula)
To calculate power bank watt-hours (Wh) from milliamp-hours (mAh), multiply capacity in mAh by the internal nominal lithium cell voltage (3.7V) and divide by 1,000: Technical references and safety provisions are standardized in the Federal Aviation Administration (FAA) PackSafe Lithium Battery Aviation Rules.
Where:
- Capacity in mAh = advertised milliamp-hour rating printed on the power bank
- Nominal Voltage (3.7V) = standard electrochemical potential of internal lithium-ion / lithium-polymer pouch cells ($3.7\text{V}$ nominal, $4.2\text{V}$ fully charged, $3.0\text{V}$ depleted)
- 1,000 = conversion factor from milliamp-hours to amp-hours ($1\text{ Ah} = 1,000\text{ mAh}$)
Scenario: You purchase a 20,000 mAh portable charger. Calculate its true stored energy in watt-hours and determine its usable 5V USB output capacity.
$\text{Wh} = [20,000\text{ mAh} \times 3.7\text{V}] ÷ 1,000 = \mathbf{74.0\text{ Watt-Hours}}$
Step 2: Account for DC-to-DC boost converter losses (~85% efficiency):
$\text{Usable Wh} = 74.0\text{ Wh} \times 0.85 = \mathbf{62.9\text{ Usable Wh}}$
Step 3: Convert usable energy back to 5V USB output capacity:
$\text{Effective 5V mAh} = (62.9\text{ Wh} ÷ 5\text{V}) \times 1,000 = \mathbf{12,580\text{ mAh at 5V}}$
Takeaway: A 20,000 mAh power bank delivers approximately 12,580 mAh of actual charge to your phone at 5V, not 20,000 mAh.
Power Bank Capacity Comparison Chart & FAA Flight Regulations
The Federal Aviation Administration (FAA), TSA, and IATA strictly regulate lithium battery transport on commercial passenger aircraft based on Watt-Hour (Wh) ratings: Regulatory guidelines and benchmarking data are published by the Transportation Security Administration (TSA) Lithium Ion Battery Travel Guidelines.
| Advertised mAh (@ 3.7V) | Stored Energy (Wh) | Usable Output (@ 85%) | FAA / TSA Carry-On Status | Checked Luggage Status |
|---|---|---|---|---|
| 5,000 mAh | 18.5 Wh | 15.7 Wh | Allowed (Unlimited quantity) | Strictly BANNED |
| 10,000 mAh | 37.0 Wh | 31.5 Wh | Allowed (Unlimited quantity) | Strictly BANNED |
| 20,000 mAh | 74.0 Wh | 62.9 Wh | Allowed (Unlimited quantity) | Strictly BANNED |
| 26,800 mAh | 99.16 Wh | 84.3 Wh | Maximum Allowed (< 100 Wh limit) | Strictly BANNED |
| 30,000 mAh | 111.0 Wh | 94.4 Wh | Airline Approval Required (100–160 Wh) | Strictly BANNED |
| 40,000 mAh | 148.0 Wh | 125.8 Wh | Airline Approval Required (Max 2 units) | Strictly BANNED |
| 50,000 mAh+ | 185.0 Wh+ | 157.3 Wh+ | Prohibited on passenger flights (>160 Wh) | Strictly BANNED |
Aviation Rule: The international limit for unrestricted passenger carry-on baggage is exactly 100 Watt-Hours. This is why high-end travel power banks are universally sized to 26,800 mAh or 27,650 mAh (99.9 Wh).
Device Recharges Estimator: How Many Times Can It Charge Your Gear?
To calculate how many full 0% to 100% recharges a power bank can deliver, divide usable watt-hours by device battery capacity:
| Device Model | Battery Capacity (Wh) | 10,000 mAh Bank (31.5 Wh Usable) | 20,000 mAh Bank (62.9 Wh Usable) | 26,800 mAh Bank (84.3 Wh Usable) |
|---|---|---|---|---|
| iPhone 16 Pro | 13.8 Wh (3,582 mAh) | 2.3 Full Charges | 4.5 Full Charges | 6.1 Full Charges |
| Samsung Galaxy S24 Ultra | 19.3 Wh (5,000 mAh) | 1.6 Full Charges | 3.2 Full Charges | 4.3 Full Charges |
| Google Pixel 9 Pro | 18.1 Wh (4,700 mAh) | 1.7 Full Charges | 3.4 Full Charges | 4.6 Full Charges |
| iPad Air 11-inch (M2) | 28.9 Wh (7,606 mAh) | 1.1 Full Charges | 2.1 Full Charges | 2.9 Full Charges |
| MacBook Air 13-inch (M3) | 52.6 Wh | 0.6 Partial Charge (60%) | 1.2 Full Charges | 1.6 Full Charges |
Using high-speed USB-PD fast charging (such as 30W or 65W output) generates slightly higher heat dissipation in the power bank, reducing effective conversion efficiency from ~88% down to ~80%.
Frequently Asked Questions About Power Banks
How many phone charges does a 20,000 mAh power bank give?
A 20,000 mAh power bank provides approximately 3–4 full charges for a phone with a 5,000 mAh battery, or about 5–6 charges for a phone with a 3,000 mAh battery. Actual charges are less than the simple mAh ratio due to voltage conversion losses (typically 10–15%).
Why does my power bank charge my phone fewer times than expected?
Power banks lose 10–20% of their energy during the voltage conversion from 3.7V (cell voltage) to 5V (USB output). Additional losses come from heat, cable resistance, and the phone's own charging circuit. A 20,000 mAh bank rated at 3.7V only delivers about 14,800 mAh at 5V.
Can I take a power bank on an airplane?
Yes, if it's under 100 Wh (approximately 27,000 mAh at 3.7V). Power banks must be in your carry-on luggage, never checked baggage. Power banks between 100–160 Wh require airline approval. Most airlines follow IATA/FAA regulations.
Is mAh or Wh a better measure of power bank capacity?
Wh (watt-hours) is the more accurate measure because it accounts for voltage. A 10,000 mAh power bank at 3.7V has the same energy as 37 Wh, but mAh alone doesn't tell you the voltage. Two power banks with the same mAh but different voltages have different energy capacities.
How long does a 10,000 mAh power bank take to charge?
A 10,000 mAh power bank takes 2–6 hours to fully charge, depending on the input power. With a 5V/2A (10W) charger: ~5 hours. With an 18W USB-C PD charger: ~2.5 hours. With a 5V/1A charger: ~8+ hours.
Can I charge a laptop with a power bank?
Yes, if the power bank supports USB-C PD (Power Delivery) output at 20V. You need a power bank with at least 45W USB-C PD output. A 20,000 mAh (74 Wh) power bank can add roughly 1–2 hours of use to a typical ultrabook.