Charge is not energy
Use the same voltage basis as the capacity claim. If the maker does not publish it, look for an explicit Wh rating or ask before converting.
Convert it
1,021.2 Whest.. Show source
estimated sourcebatteryrank.com2026-08-06https://batteryrank.com/methodologyWh = (mAh × volts) ÷ 1,000. The initial voltage of 3.7 V is a planning example. Enter the voltage used for the manufacturer’s capacity rating; do not infer it from the USB port.
Comparing a power bank with a power station
99.2 Whest.. Show source
estimated sourcebatteryrank.com2026-08-06https://batteryrank.com/methodologyThe energy that reaches your device can be lower because of conversion losses and use while charging. Stored Wh is a useful starting comparison; it does not promise a number of phone recharges.
The same energy, quoted three ways
| Quoted at | mAh for ~1,024Wh | Comparison |
|---|---|---|
| 3.7 V assumed | 276,757 mAhest.. Show sourceestimated sourcebatteryrank.com2026-08-06https://batteryrank.com/methodology | Same stored energy |
| 11.1 V assumed | 92,252 mAhest.. Show sourceestimated sourcebatteryrank.com2026-08-06https://batteryrank.com/methodology | One-third the mAh at three times the voltage |
| 25.6 V assumed | 40,000 mAhest.. Show sourceestimated sourcebatteryrank.com2026-08-06https://batteryrank.com/methodology | Lower mAh at a higher voltage |
Each row represents 1,024 Wh at a different assumed voltage. These calculated figures do not describe the physical wiring or measured capacity of a product.
Airline limits use watt-hours
FAA guidance requires spare batteries and power banks in carry-on baggage, with terminals protected. The general lithium-ion limit is 100 Wh; larger spare batteries up to 160 Wh require airline approval, with a limit of two. Airlines can impose stricter power-bank rules.
| Example charge | Calculated stored energy | What to check |
|---|---|---|
| 10,000 mAh | 37 Whest.. Show sourceestimated sourcebatteryrank.com2026-08-06https://batteryrank.com/methodology | Actual marked Wh and airline policy |
| 27,000 mAh | 99.9 Whest.. Show sourceestimated sourcebatteryrank.com2026-08-06https://batteryrank.com/methodology | Voltage basis, actual marked Wh and airline policy |
| 40,000 mAh | 148 Whest.. Show sourceestimated sourcebatteryrank.com2026-08-06https://batteryrank.com/methodology | Larger-battery approval and carrier restrictions |
| 50,000 mAh | 185 Whest.. Show sourceestimated sourcebatteryrank.com2026-08-06https://batteryrank.com/methodology | Above the FAA general spare-battery approval range |
Rules: FAA PackSafe lithium-battery guidance, reviewed October 8, 2026. The table is arithmetic at an explicitly assumed voltage, not product certification or airline acceptance.
A household power station can exceed passenger-baggage limits by a wide margin. Check its actual marked Wh before planning to fly with it; a different bag or an mAh conversion does not change its stored energy.
Working backwards from your device
Read the device’s own battery rating and the bank’s capacity basis. Then look for usable output-energy evidence for the charging path you will use. Conversion losses and device operation while charging affect the result; one assumed loss percentage cannot describe every USB, DC and AC setup.
| Reading | Useful for | Limit |
|---|---|---|
| Rated stored Wh | Comparing the stated energy in two batteries | Not a measurement of energy delivered to the device |
| Delivered energy on the chosen output path | Estimating energy available for charging | Depends on the measurement conditions and load |
| Device battery Wh and use while charging | Understanding the demand | An idle recharge and active use can need different energy |
For household AC appliances, use AC-delivered capacity rather than treating rated battery energy as outlet energy. Our Wh vs W guide explains the distinction, and the sizing tool starts with your load list.
If the label figures disagree
The conversion is only as reliable as its inputs. If the published mAh and Wh disagree, ask the manufacturer to explain the difference. A calculated answer cannot verify a capacity claim.
Our model pages show rated capacity alongside its source and date. AC-delivered energy is labeled separately as measured or estimated.
Frequently asked questions
- How do you convert mAh to Wh?
- Multiply the milliamp-hours by the pack voltage, then divide by 1,000. For example, 20,000 mAh at an assumed 3.7 V gives (20,000 × 3.7) ÷ 1,000 = 74 Wh. Use the voltage published with your product’s capacity rating.
- Why does my power bank say 20,000mAh but only charge my phone twice?
- The mAh rating needs its stated voltage before it describes stored energy. That stored energy is not all delivered to the phone: conversion losses and the phone’s use while charging affect the result. Do not infer a recharge count from mAh alone or assume one USB voltage for every charging mode.
- Is a higher mAh always better?
- At the same voltage, a larger mAh rating represents more stored energy. Across different voltages, convert to Wh first. For example, tripling the voltage while dividing mAh by three gives the same energy; neither number alone establishes the product’s delivered capacity.
- What voltage should I use if the manufacturer does not say?
- Use the voltage basis published with the capacity claim, or ask the maker for the Wh rating. The converter starts with an illustrative voltage; it is not an inferred specification for your product. A USB output voltage may differ from the voltage behind the capacity claim.