What is H2testw and where do I get it?

A free Windows utility, widely used in the industry, that verifies the real capacity of a flash device by writing and reading back the whole card. It is the standard first check buyers run on an incoming batch. It works on any card from any supplier, which is exactly why we point buyers to it.

How many units from a batch should I test?

There is no single correct number — it depends on batch size and how much risk you carry downstream. Testing a sample from the start, middle and end of a run is a practical starting point, and worth doing on the first order from any new supplier.

Can a card pass capacity testing and still fail in the field?

Yes. Capacity is one failure mode. Endurance under continuous overwrite, temperature behaviour and controller compatibility with your host are separate ones, and they are what matter most for recording and embedded applications.

Do you test before shipping?

Capacity and read/write verification run as part of our production flow before packing. We also recommend you verify independently on receipt — see our quality control page for what we check and what we cannot yet document.

What should I ask a supplier to put in writing about testing?

What is tested, at which stage, against what criteria, and what happens to a batch that fails. A supplier that cannot describe its own test in those terms is telling you something.

How to Test a Memory Card Before You Accept a Batch

In short

The single most useful test on a memory card is a full capacity write-and-read-back. H2testw is a free Windows tool that does exactly this: it writes data across the whole card, reads it back, and reports any capacity that is not really there. A card that reports 64GB to the operating system but can only hold 8GB will pass a drag-and-drop spot check and fail this test in minutes. Run it on a sample from every batch, from every supplier, including ours. Speed and endurance need different tools, and for continuous recording workloads — dashcams, IP cameras — endurance matters more than peak speed.

The tests, and what each one catches

Test	Tool	How	What it catches	Time
Capacity verification	H2testw (Windows, free)	Write test data across the full card, read it back, compare. The tool reports real capacity and any data corruption.	Overstated capacity — the most reported problem in this product category.	Depends on card size and write speed; a 64GB card typically takes tens of minutes.
Read / write speed	CrystalDiskMark, or H2testw’s own speed output	Measure sequential and random read/write against the class the card is specified to meet.	A card sold as U3 or V30 that does not sustain the rate it claims.	Minutes.
Sustained write under continuous load	Looped write on the actual target device	Record continuously on the dashcam or camera the card is destined for and watch for dropped frames or write errors.	Cards that benchmark well but cannot hold a continuous write without buffer stalls.	Hours — this is the test that matters for video workloads.
Endurance / overwrite cycle	Controlled overwrite until failure, on a sample basis	Repeatedly fill and erase the card and monitor for bad-block growth and write failure.	Cards that will not survive the overwrite duty cycle of 24/7 recording.	Days to weeks. Run on samples, not on every unit.
Temperature behaviour	Chamber or in-device thermal soak	Run the card at the top and bottom of the intended operating range and check for enumeration or write errors.	Cards that fail in a vehicle in summer or in an outdoor enclosure in winter.	Hours.

Capacity verification, step by step

Install H2testw Free Windows utility. No installer bundling, no account.
Select the card, not your disk The tool writes to the target — check the drive letter twice.
Write and read back the full capacity Choose “all available space” and run.
Read the result A clean result reports the full verified capacity with no errors. Any shortfall or corruption means the card does not hold what it claims.

Signs of an overstated-capacity card

The card reports its advertised capacity to the operating system but errors part-way through a large copy.
Write speed collapses after the first few gigabytes — the classic signature of a card whose real capacity is smaller than its label.
The label and packaging look right but the card has no identifiable markings under magnification.
The price is far below the prevailing market for that capacity — flash has a material cost floor.

None of these prove a card is bad on their own. Together they are the pattern buyers report before a capacity test confirms it.

Match the test to the workload

Dashcam and vehicle recording

Continuous overwrite, wide temperature range, vibration. Endurance and sustained write matter more than peak speed. See memory cards for dashcams.

Security and IP cameras

24/7 overwrite cycles. Test sustained write on the actual device, not on a desktop card reader. See memory cards for security cameras.

IoT and embedded

Boot and data storage with a fixed part. Enumeration reliability on the host matters more than raw throughput. See embedded flash storage.

Promotional and branded drives

Intermittent use, but a failure damages the brand it was meant to promote. Capacity verification is the check that matters here.

Ask us what we test on your batch

Send your acceptance criteria with the enquiry and we will confirm how the batch is checked. We reply to business enquiries within 1 business day.

Request a quote