This article covers Cooler Master MasterBox Q300L ミニタワー型PCケース MCB-Q300L-KANN-S00 CS7251.

Overview

The Cooler Master MasterBox Q300L is a compact mini tower PC case that offers excellent expandability and thoughtful design at an affordable price. It supports microATX and Mini-ITX motherboards and features a large clear side panel and geometric magnetic dust filters. The case can be placed vertically or horizontally, and the I/O panel can be repositioned thanks to its modular design. This case is ideal for entry-level to mid-range gaming PC builds or space-constrained desktops. It can accommodate graphics cards up to 360mm long and a 240mm radiator in the front, allowing for relatively high-end components despite the compact size. The Q300L also includes cable management provisions, making it suitable for both beginners and experienced builders. The simple black exterior blends well with any room.

Compatibility Guide

The MasterBox Q300L supports microATX and Mini-ITX motherboards. It uses a standard ATX power supply in a bottom-mount configuration. Maximum GPU length is 360mm, and CPU cooler clearance is 157mm, so many high-end components will fit. Storage options include two 3.5-inch bays and two 2.5-inch bays (four drives total). Cooling support: front 240mm radiator, rear 120mm fan, top two 120mm fans. Note that ATX motherboards are not supported, and the bottom-mounted PSU may require longer cables on some units.

Product Info

The MasterBox Q300L (model MCB-Q300L-KANN-S00) is a mini tower PC case from Cooler Master. Its dimensions are 387 x 230 x 381 mm (WxHxD) and it weighs approximately 4.4 kg. It is priced very competitively at around ¥3,929 on Japan, and the authorized Japanese version (CS7251) comes with a 2-year warranty. Its market position is entry-level to mid-range, standing out through its magnetic dust filters and modular I/O panel at a low price point. Although launched several years ago, it remains popular due to its excellent price-to-performance ratio. The case is constructed from steel and plastic, with a mesh front panel for airflow. The clear side window lets you showcase internal components.

Best Use Cases

First-time PC builder on a budget: The case offers good expandability and cable management at a very low price, reducing the stress of any building mistakes. Perfect for learning. User needing a space-saving desktop: Its compact mini tower footprint fits easily on a desk or in a small space, and the ability to place it vertically or horizontally adds layout flexibility. Budget-conscious gamer: With support for GPUs up to 360mm, the Q300L can house mid-range to upper-mid-range gaming cards. Build a capable gaming rig without spending much on the case. Not for: High-end air coolers over 157mm tall, radiators larger than 240mm, or ATX motherboards. Also not ideal for builds requiring extensive storage (more than 4 drives) or multiple top-mounted radiators. ## Alternatives
In the same price bracket, the Fractal Design Focus G Mini and the Thermaltake Versa H18 are direct competitors. The Focus G Mini offers better cable management and airflow but costs slightly more. The Versa H18 has a similar mesh front design but lacks magnetic dust filters. The MasterBox Q300L stands out with its unique features like magnetic filters and a repositionable I/O panel, and it is usually the cheapest option. However, if airflow is your top priority, the Fractal Design may be a better choice despite the higher price.

Things to Consider

Airflow is decent but not outstanding; the magnetic dust filters add some restriction. For high-end components under heavy load, consider adding extra fans or a front-mounted AIO. Interior space is moderately tight; cable management can be a bit messy without modular PSU cables or careful routing. The case only includes one rear 120mm fan; you will need to purchase additional fans for front intake (ideally two 120mm) to maintain positive pressure. When placed vertically, the case is stable enough with standard components, but a heavy GPU and large CPU cooler might raise the center of gravity slightly. ## FAQ Q: Can I install an ATX motherboard in this case? A: No, only microATX and Mini-ITX are supported. ATX boards will not fit physically. Q: How many case fans come with the Q300L? A: Only one 120mm fan is included (rear exhaust). You should buy additional fans for the front and top. Q: Can I mount a 360mm radiator? A: No, the maximum radiator size is 240mm (front mount only). The rear and top cannot accommodate radiators.

Product Disclosure (Amazon)

  • Manufacturer: Cooler Master
  • ASIN: B0785GRMPG
  • Note: This article covers a manufacturer-made product based on Amazon listing details.