The Lian Li B4-mATX is a compact 21.3-liter mATX case that Lian Li developed in collaboration with DAN Cases. The best part: You can use it horizontally as a desktop or rotate it 90 degrees to set it up vertically—in the vertical configuration, it takes up about 30 percent less space on your desk. Despite its compact dimensions, it accommodates full-size graphics cards up to 358 mm, mATX motherboards, and either an ATX or SFX power supply. Prices start at 69.99 euros.
Lian Li and DAN Cases have been collaborating for some time, and the B4-mATX is the latest result of this partnership. As usual, Daniel Hansen from DAN Cases is leading the project. Anyone who likes small-form-factor builds but doesn’t want to compromise on high-end hardware should take note.
One case, two orientations
The key feature of the B4-mATX is its dual-use design. When laid flat, it serves as a slim desktop unit on your desk. When stood upright, its footprint shrinks by about 30 percent. Lian Li has thought this through to ensure it works in everyday use: The swivel power connector can be rotated outward for easy access to the cable, or inward to tuck excess cable length inside the case when the unit is in portrait mode.
Below the PCIe slots, there’s also a swiveling cable holder that presses rear I/O and power cables flat against the case in vertical mode. The total space here, including connectors, is a maximum of 52 mm—so if you’re using a thick HDMI or DisplayPort cable, you should keep that in mind. For the front panel, you can choose between perforated mesh for direct airflow and a real wood front panel in walnut or beech. Both options are available in black and white.
ATX or SFX, Air or Water
Two slim 120-mm fans (120 × 120 × 15 mm, without RGB) are pre-installed as exhaust fans on a removable mount inside the case. The front slim fan can be flipped around and used as an intake fan once an air cooler is installed. There are dedicated mounts for the power supply that accommodate either an SFX power supply or an ATX power supply up to 140 mm in length.
When it comes to cooling, the power supply determines the options. With an SFX power supply, a radiator up to 360 mm (maximum 52 mm thick) fits on the side; with a 140-mm ATX power supply, the maximum is 240 mm. A reversible rear fan mount swivels inward to improve airflow for tower air coolers, or outward to make room for a side-mounted AIO. In total, up to nine fans can be distributed across the top, side, bottom, rear, and front.
Compact Dimensions, Full-Size Hardware
The real challenge with such a small case is compatibility—and this is where the B4-mATX delivers. With a volume of 21.3 liters, it accommodates graphics cards up to 358 mm in length across four expansion slots, as well as CPU air coolers up to 162 mm in height (or 168 mm if you remove the side fan mount). A height-adjustable anti-sag bracket to prevent the graphics card from sagging is pre-installed; the adjustable support arm touches the card without getting in the way of the fans.
As for storage, the options are naturally limited: a 3.5-inch HDD or a 2.5-inch SSD at the bottom, plus an additional 2.5-inch SSD at the front. This is usually more than enough for a compact gaming or work system.
Key specifications at a glance
| Feature | Lian Li B4-mATX |
|---|---|
| Volume | 21.3 liters |
| Dimensions (D×W×H) | 406.95 × 191 × 207.5 mm |
| Material | 4.0 mm steel (Mesh) / steel + wood (Wood) |
| Motherboard | Micro-ATX / Mini-ITX |
| Expansion slots | 4 |
| GPU length | up to 358 mm |
| CPU cooler height | up to 162 mm (168 mm without side fan mount) |
| Power Supply | ATX (up to 140 mm) / SFX |
| Radiator (side-mounted) | up to 360 mm (SFX) / up to 240 mm (ATX) |
| Fans | Up to 9; two 120-mm slim fans pre-installed |
| I/O | 2× USB 3.0 Type-A, 1× USB 3.2 Type-C, Audio, Power |
| Warranty | 1 year |
Optional accessory: the B4-mATX Vertical AeroDeck
If you want to use the case in a vertical orientation, you can optionally purchase the B4-mATX Vertical AeroDeck. This accessory creates a direct airflow path to the graphics card and expands the cooling capacity by up to three 120-mm or two 140-mm fans. It comes with tempered glass side panels that showcase the installed fans and a magnetic PVC dust filter. Visually, the AeroDeck matches the Wood variant and is also available in walnut or beech, as well as in black and white.
How does the B4-mATX perform in tests?
Initial international reviews have been positive. TweakTown built a system with an AMD Ryzen 9 7900 and measured an average CPU temperature of around 62 °C during a seven-hour stress test —a good result for a case of this size, thanks primarily to the heavily perforated panels and the two pre-installed slim fans. Even a power-hungry Zotac RTX 3090 remained within safe operating limits. In its review, TechPowerUp praises the well-thought-out case design and the aggressive entry-level price of around $70.
However, there is one compromise: If you really want to install a 360-mm radiator, you’ll have to opt for an SFX power supply and choose an AIO with a slim 25-mm profile. For a 21-liter case, though, that’s more nitpicking than a real shortcoming.
Pricing and Availability of the Lian Li B4-mATX
The Lian Li B4-mATX has been available since June 26, 2026. The MSRP is as follows:
- B4-mATX Mesh Black: 69.99 euros
- B4-mATX Mesh White: 74.99 euros
- B4-mATX Wood Black: 84.99 euros
- B4-mATX Wood White: 89.99 euros
- B4-mATX Vertical AeroDeck (Black/White): 29.99 euros
These models are already listed on Caseking: Mesh Black, Mesh White, Wood Black (walnut), Wood White (beech), and the AeroDeck in black and white. Full details and additional images are available on Lian Li’s official product page.
Conclusion on the Lian Li B4-mATX
With the Lian Li B4-mATX, SFF enthusiasts get a flexible case that can be used either horizontally or vertically and accommodates a surprising amount of hardware—from a 358-mm graphics card to a 360-mm radiator. The wooden front panel is a nice touch for anyone who finds a mesh-only design too technical. With a starting price of 69.99 euros, this is an attractive offering that further shakes up the already vibrant market for compact mATX cases.
