What Does mAh Mean on a Power Bank? The Complete Guide
QUICK ANSWER
What does mAh mean? mAh stands for milliampere-hours — it measures how much electrical charge a battery can store. A 10,000mAh power bank can theoretically deliver 10,000mA (10 amps) for one hour, or 1,000mA for 10 hours. But the rated number is NOT what your phone receives — due to the 3.7V to 5V voltage step-up conversion inside every power bank, you only get about 60-70% usable capacity. A "10,000mAh" bank delivers roughly 6,000-7,000mAh to your devices. Use the formula: Usable mAh = (Rated mAh × 3.7V × 0.85) ÷ 5V.
Table of Contents
1. What Is a Milliampere-Hour (mAh)?
A milliampere-hour (mAh) is a unit of electric charge. It tells you how much current a battery can supply over time:
- 1,000 mAh = can deliver 1,000mA (1 amp) for 1 hour
- 10,000 mAh = can deliver 10,000mA for 1 hour, OR 1,000mA for 10 hours
- 20,000 mAh = can deliver 20,000mA for 1 hour, OR 1,000mA for 20 hours
Think of mAh like the size of a water tank. A bigger tank (higher mAh) holds more water (charge), but how fast the water flows (wattage) is a separate specification. A power bank can have high mAh but slow charging speed — or vice versa. Both numbers matter.
The "milli" prefix means one-thousandth. 1,000 milliamps = 1 amp. So a 10,000mAh battery stores the same charge as a 10Ah (amp-hour) battery. The mAh unit is used because it produces friendlier numbers for consumer electronics — "10,000mAh" reads better than "10Ah" on a product box.
2. Rated vs Usable Capacity: Why You Lose 30-40%
This is the single most important thing to understand about power bank specifications — and the one manufacturers don't advertise prominently.
The 3.7V → 5V Problem
Lithium-ion and lithium-polymer cells operate at a nominal voltage of 3.7V. This is the voltage at which mAh capacity is measured and advertised. But USB output requires 5V (or higher — 9V, 15V, 20V for fast charging). To bridge this gap, every power bank contains a boost converter circuit that steps up the voltage. This conversion is not free — it costs 15-35% of the stored energy, lost as heat.
At 3.7V: 10,000mAh × 3.7V = 37 watt-hours (Wh) of stored energy
At 5V output: the same 37Wh ÷ 5V = 7,400mAh theoretical maximum
After efficiency losses (~85%): 7,400 × 0.85 = ~6,290mAh actually delivered
Efficiency Varies by Quality
| Power Bank Tier | Conversion Efficiency | 10,000mAh → Usable |
|---|---|---|
| Premium (GaN, quality components) | 88-92% | ~6,500-6,800mAh |
| Mid-range (standard quality) | 75-85% | ~5,500-6,300mAh |
| Budget / No-name | 60-70% | ~4,400-5,200mAh |
This is why two "10,000mAh" power banks can deliver noticeably different real-world performance. The efficiency of the boost converter circuit and the quality of the battery cells matter enormously.
3. The Conversion Formula (With Examples)
THE FORMULA
Usable mAh = (Rated mAh × 3.7V × Efficiency) ÷ Output Voltage
For standard 5V USB output with 85% efficiency:
Usable mAh = Rated mAh × 0.629
Example 1: 5,000mAh Bank
(5,000 × 3.7 × 0.85) ÷ 5 = ~3,145mAh usable — about 1 full iPhone charge
Example 2: 10,000mAh Bank
(10,000 × 3.7 × 0.85) ÷ 5 = ~6,290mAh usable — about 1.5-2 iPhone charges
Example 3: 20,000mAh Bank
(20,000 × 3.7 × 0.85) ÷ 5 = ~12,580mAh usable — about 3-4 iPhone charges
4. mAh vs Wh: Which Matters More?
Watt-hours (Wh) is the more honest unit for comparing battery capacity because it accounts for voltage differences. Here's why:
mAh (Milliampere-Hours)
Pros: Familiar, easy to compare within the same voltage category
Cons: Misleading when comparing devices with different voltages. A 5,000mAh laptop battery at 11.4V stores 57Wh — more energy than a 10,000mAh power bank at 3.7V (37Wh). mAh alone doesn't tell the full story.
Wh (Watt-Hours)
Pros: Voltage-independent — directly compares total energy regardless of battery chemistry or device type
Cons: Less familiar to consumers. Used by airlines for safety regulations (100Wh carry-on limit).
mAh → Wh Conversion
Wh = (mAh × Voltage) ÷ 1,000
10,000mAh @ 3.7V = 37Wh · 20,000mAh @ 3.7V = 74Wh · 27,000mAh @ 3.7V = 99.9Wh (airline limit)
5. How Many Phone Charges Per Capacity Tier
| Power Bank | iPhone 16 (~3,300mAh) | Galaxy S25 (5,000mAh) | Pixel 9 Pro (~4,700mAh) | iPad Air (~7,500mAh) |
|---|---|---|---|---|
| 5,000mAh | ~0.9 | ~0.6 | ~0.6 | ❌ |
| 10,000mAh ★ | ~1.9 | ~1.3 | ~1.3 | ~0.8 |
| 20,000mAh | ~3.8 | ~2.5 | ~2.7 | ~1.7 |
| 27,000mAh | ~5.1 | ~3.4 | ~3.6 | ~2.3 |
*Assumes 65% overall efficiency (budget to mid-range conversion). Premium GaN power banks will achieve ~10-15% more charges. Real-world results vary with ambient temperature, cable quality, and whether the phone is in use while charging.
6. Common mAh Myths Debunked
Myth: "20,000mAh = twice the charges of 10,000mAh"
Mostly true — in theory. But real-world factors (efficiency curves, heat, device charging behavior) mean the relationship is close but not perfectly linear. A 20,000mAh bank typically delivers 1.8-2× the usable capacity of a 10,000mAh bank from the same brand.
Myth: "Higher mAh = faster charging"
False. mAh measures capacity (how much), not speed (how fast). Charging speed is determined by output wattage (W). A 20,000mAh bank with 10W output charges slower than a 10,000mAh bank with 30W output. Always check both specifications.
Myth: "A 10,000mAh bank always charges a 5,000mAh phone twice"
False. With 65% efficiency: (10,000 × 0.65) ÷ 5,000 = 1.3 charges. You'd need a ~15,400mAh bank for two full charges of a 5,000mAh phone.
More resources: Now that you understand mAh, read our How to Choose a Power Bank: Complete Buyer's Guide for wattage, port selection, and feature recommendations, or explore Power Bank Specs Guide for a technical deep-dive into charging protocols.
WOWOHCOOL FACTORY STAT
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Supply Chain Expert · Wireless Charging Specialist
Nina Nico is a supply chain management expert with 10+ years experience helping global B2B clients source quality power banks from WOWOHCOOL — a premium charging solution specialist in Shenzhen, China. She holds a degree in International Trade and is a certified supply chain professional (CSCP).