How to check real USB capacity (Detect fake USB with 100% accuracy)

Did you just buy a 128GB, 256GB or even 1TB USB drive on e-commerce platforms at a "shockingly cheap" price? When you plug it into your computer, Windows still shows the full capacity, but when you copy data to it, files get corrupted, videos won't play, or data just vanishes?

You most likely bought a fake-capacity USB drive (hacked firmware). In this guide, SonVuDev will show you the most accurate ways to check the real USB capacity to avoid wasting money and protect your important data.

Why do fake USB drives still show full capacity on my computer?

Many people wonder: "Why does my computer still report 128GB when the drive is actually fake?".

The trick used by fake USB manufacturers is to use a low-capacity memory chip (for example, only 8GB) but hack the chip's firmware (controller) to deceive Windows, macOS or Linux. When you plug it in, the computer reads the hacked firmware information and displays the fake number (128GB, 256GB).

However, when you copy data exceeding the real capacity (over 8GB), the memory overflows. Files copied afterward overwrite old files or become corrupted and unreadable.

Common methods to check real USB capacity

To accurately determine whether your portable drive or USB is "capacity-faked", you cannot rely on visual inspection — you need data read/write tools that test the actual memory cells.

1. Check with the classic H2testw tool (Free)

H2testw is a very old German tool that works by writing .h2w files to fill the USB, then reading them back to see if any partitions are faulty.

• Pros: High accuracy, completely free.
• Cons: Extremely slow scanning. If you own a USB that claims a fake capacity of 512GB or 1TB with low write speed (fake USBs often use very poor memory chips), you may have to leave your computer running from 5 hours to a full day just to get a result. The interface is also outdated and complicated for beginners.

2. Quick check with ChipEasy or Flash Drive Information Extractor

These tools work by reading chip information (PID/VID) from the original manufacturer to determine the real capacity of the memory chip inside.

• Pros: Instant results within seconds.
• Cons: Fake USB manufacturers have become much more sophisticated. They can block or even fake the PID/VID codes, making chip-reading tools no longer 100% accurate.

Spark Capacity Tester — Next-generation USB capacity checking, super fast

If you don't want to waste hours waiting for old software to scan every gigabyte, or worry about chip-reading tools being bypassed, then Spark Capacity Tester (developed by SonVuDev) is the optimal solution for you.

View Spark Capacity Tester details here

Why choose Spark Capacity Tester over other tools?

Designed with minimalism and high performance in mind, this software completely solves the inconveniences of traditional tools:

• Quick Size Test mode (Exclusive): No need to wait for a full write on huge drives. The built-in smart algorithm quickly tests data across the entire 1TB drive in just a few minutes, instantly detecting hacked firmware.
• Full Free Space Test: Deep scan of all remaining free space, automatically detects faulty memory areas accurately and gives clear PASS/FAIL results.
• No installation needed (Portable): Just a single executable file, download and use immediately. No ads, no bloatware installed on your computer.

For a very small cost ($3.99 USD / 99,000 VND), you own a lifetime checking tool that saves you from scams buying fake USBs worth hundreds of thousands or millions of dong online.

Frequently Asked Questions (FAQ)

Can a fake-capacity USB be restored to its real capacity?

You can use firmware flashing tools (like MPTool) to restore the USB to its real capacity (for example, back to 8GB). However, the memory chip in fake USBs is usually rejected/old stock with very poor durability and slow speed. You should not store important data on these devices.

Does Spark Capacity Tester support memory cards (MicroSD)?

Yes. The software supports checking all portable storage devices connected via USB including: Portable HDD/SSD, USB drives, and Memory cards (via card reader).

What operating systems does this software support?

Currently, Spark Capacity Tester v1.4.0 is optimized for Windows operating systems.