Cooler Master
Cooler Master MasterBox Q300L Micro-ATX PC Case
Bottom line: The Cooler Master MasterBox Q300L Micro-ATX PC Case ($29.99 on Amazon as of 2026-10-06): Fits a full standard ATX PSU up to 160mm despite the compact mATX cube footprint; main trade-off: only one 120mm fan included, so airflow builds need fans purchased separately.
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*Price sourced from Amazon.com. Last updated 2026-10-06. Price and availability subject to change.
Pros & Cons
Pros
- ✓ Fits a full standard ATX PSU up to 160mm despite the compact mATX cube footprint
- ✓ I/O panel repositions to six spots: front, top, or bottom on either side
- ✓ 360mm GPU and 159mm CPU cooler clearance handles most mainstream parts
- ✓ Supports a 240mm AIO and up to five fans; one 120mm fan pre-installed
Cons
- ✗ Only one 120mm fan included, so airflow builds need fans purchased separately
- ✗ Perforated panels on all sides let more noise escape than a solid-panel case
- ✗ Micro-ATX and Mini-ITX only, so no full ATX motherboard support
- ✗ No RGB lighting or fan controller, unlike pricier cases in this bracket
Manufacturer description
Inside the compact frame you can mount Micro-ATX or Mini-ITX boards alongside a full standard ATX power supply up to 160mm long, which is unusual for a case this size. Clearance is generous where it counts: CPU coolers up to 159mm tall, graphics cards up to 360mm, and support for a 240mm liquid cooler plus up to five fans total, with one 120mm fan pre-installed out of the box. The defining trick is the modular I/O panel. Cooler Master lets you reposition it to the front, top, or bottom on either side of the chassis, six placements in all, so your ports land wherever your desk setup actually…
SpecPicks Verdict
SpecPicks scored Cooler Master MasterBox Q300L Micro-ATX PC Case using a rating × review-volume × price-fit model applied to published specs and reviews across the pc cases category. Cooler Master's pc cases lineup sits within the broader category mid-tier; price and specs are the deciding factors over brand loyalty here. Judge it on the specification table and the price rather than on sentiment: check the figures that decide your use case, then put it side-by-side with two or three close alternatives in the Compare tool before clicking through.
Common buyer scenarios for pc cases of this kind: matching it to an existing build, replacing a failing part, or upgrading from a previous-generation equivalent. Check the spec table below against your current setup — particularly socket / form-factor / power-rating fields — and confirm compatibility on the retailer's listing before purchase. Prices and stock are set by the retailer and may have moved since this page was last updated.
Frequently Asked Questions
Will a full-size graphics card fit in the Q300L?
Cooler Master rates the Q300L for GPUs up to 360mm long, which covers most mainstream dual- and triple-fan cards. Measure your specific card first, since some flagship models exceed that.
Does the Q300L take a standard ATX power supply?
Yes. Cooler Master specifies support for a PSU up to 160mm in length, so a standard ATX unit fits rather than requiring an SFX supply like many cases this size.
How many fans come with the case?
One 120mm fan is pre-installed. The chassis supports up to five fans total, or a 240mm liquid cooler, so plan on buying additional fans for a high-airflow build.
What motherboard sizes does the Q300L support?
Micro-ATX and Mini-ITX. Full ATX boards are not supported, so confirm your motherboard form factor before ordering.
What is the tallest CPU cooler that fits?
The listed clearance is 159mm, which accommodates most mid-tower tower coolers. Taller flagship air coolers will not clear the side panel.
Key Features
- Ample Interior: Explore ample interior space for Micro-ATX or Mini-ITX motherboards, ensuring easy and future expansion
- Components Clearance: Accommodates CPU coolers with a max height of 159mm, GPU cards up to 360mm, and PSU up to 160mm in length.
- Versatile Cooling: Maximize cooling performance with a 240mm liquid cooler and 5 fans.
- Modular I/O Panel: You have the flexibility to adjust its position at the front, top, or bottom on both sides
- Edge-To-Edge Panel: Show off your meticulous build through the transparent side panel with pride.
- Open Thermal Design: The perforated design on all sides promotes optimal airflow and heat dissipation
Full Specifications
| Brand | Cooler Master |
|---|---|
| Color | Dark Gray |
| Material | Alloy Steel, Plastic |
| Case Type | Mini-Tower |
| Model Name | Q300L |
| Model Number | MCB-Q300L-KANN-S00 |
| Compatibility | PC |
| Ample Interior | Explore ample interior space for Micro-ATX or Mini-ITX motherboards, ensuring easy and future expansion |
| Built-In Media | 1 computer case |
| Cooling Method | Air |
| Item Type Name | grocery |
| Number of Fans | 3 |
| Mfr Part Number | MCB-Q300L-KANN-S00 |
| Total Usb Ports | 2 |
| Antenna Location | Gaming |
| Modular I/O Panel | You have the flexibility to adjust its position at the front, top, or bottom on both sides |
| Versatile Cooling | Maximize cooling performance with a 240mm liquid cooler and 5 fans. |
| Compatible Devices | Micro-ATX and Mini-ITX motherboards, Cooler Master devices |
| Edge-To-Edge Panel | Show off your meticulous build through the transparent side panel with pride. |
| Enclosure Material | Alloy Steel, Plastic |
| Full listing title | Cooler Master MasterBox Q300L Micro-ATX PC Case – Compact mATX Computer Case with Magnetic Dust Filters, Modular Adjustable I/O Panel, Perforated Airflow Design, 1 x 120mm Pre-Installed Fan, Black |
Ready to buy?
Cooler Master MasterBox Q300L Micro-ATX PC Case – Compact mATX Computer Case with Magnetic Dust Filters, Modular Adjustable I/O Panel, Perforated Airflow Design, 1 x 120mm Pre-Installed Fan, Black is listed on Amazon. Price, availability, shipping and returns are set by Amazon and its sellers — check the listing for current terms. SpecPicks earns a small commission on qualifying purchases — thank you for supporting independent review work.
*Price sourced from Amazon.com. Last updated 2026-10-06. Price and availability subject to change.
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