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
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Availability:
Only 2 left in stock, order soon!
Arrives
Wednesday, Aug 5
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Style: Q300L V1
Color: Black
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
- Magnetic Dust Filters: The unique pattern of the dust filter adds a distinctive appearance to the case.
Description
The Master Box Q300L is your straightforward option in the lineup of the brand new Master Box Series from Cooler Master. A Series that might be small in size but excels in functionality and modularity without compromising on the thermal performance. Although the size wouldn't tell, the Master Box Q300L supports a standard ATX PSU which we don't see often in the market with this size. Based on the different system setup, the I/O panel can be adjusted to six different locations, three options at each side of the case. You can decide which setup fits your system best. Due to the cube design of the frame and special pattern design on the magnetic dust filter will make the chassis stand out from the rest. The combination of a practical design and the unique customizable outlook makes the Master Box Q300L The perfect choice for office and home.
Brand: Cooler Master
Motherboard Compatability: Micro-ATX and Mini-ITX
Case Type: Mini-Tower
Recommended Uses For Product: Gaming
Color: Black
Material: Alloy Steel, Plastic
Power Supply Mounting Type: Bottom Mount
Cooling Method: Air
Model Name: Q300L
Item Weight: 480 Grams
Supported Motherboard: Micro-ATX and Mini-ITX
Case Type: Mini-Tower
Power Supply Mounting Type: Bottom Mount
Cooling Method: Air
Total Expansion Slots Quantity: 4
Total USB 3.0 Ports: 2
Total Usb Ports: 2
Other Special Features of the Product: Accomodates CPU Coolers, Adjustable, Dust Filter, Edge-To-Edge Panel, Fully Ventilated
Hard Disk Form Factor: 3.5 Inches
Internal Bays Quantity: 1
Compatible Devices: Micro-ATX and Mini-ITX motherboards, Cooler Master devices
Number of Fans: 3
Power Supply Maximum Output: 500 Watts
Color: Black
Enclosure Material: Alloy Steel, Plastic
Item Weight: 480 Grams
Item Dimensions D x W x H: 15.39"D x 9.06"W x 15"H
Brand: Cooler Master
Model Name: Q300L
Manufacturer: Cooler Master
UPC: 884102095313 884102038006
Global Trade Identification Number: 06, 13, 88
Mfr Part Number: MCB-Q300L-KANN-S00
Model Number: MCB-Q300L-KANN-S00
Warranty Description: 2
Built-In Media: 1 computer case
Item Type Name: grocery
Antenna Location: Gaming
Frequently asked questions
If you place your order now, the estimated arrival date for this product is:
Wednesday, Aug 5
Yes, absolutely! You may return this product for a full refund within 30 days of receiving it.
To initiate a return, please visit our Returns Center.
View our full returns policy here.
To initiate a return, please visit our Returns Center.
View our full returns policy here.
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Top Amazon Reviews
Style: Q300L V1
Color: Black
Considering the price point, this is the best case I've ever used. Sure it isn't the best case in existence but nothing at this price beats it. Cable management is decent, it has felt plenty sturdy to trust with my components and has more space for fans than my motherboard does headers. Cooling is only limited by my issues with limited fan headers, not the case. Fit my 9070 XT no problems as well and the tower air cooler. ONly issues I've had are the weak magnets on the dust filters, and a few sharp edges that I ran into during install. Also only 2 hard drive mounts isn't ideal but hasn't been a problem.
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Reviewed in the United States on March 4, 2026 by Stephen Raman
Style: Q300L V1
Color: Black
Great value micro-atx case. Its cheap and works. Like the compact size and the fact it came with screws, spacers, ties and a fan. I like the magnetic dust filters concept however BEWARE of the very rough and pointed edges which could cut you while handling them. The power button on the side panel worked for me but could be a problem with other builds. I was barely able to fit two Thermalright TL-C14C 140mm fans in the front with the default front facing power button+LED panel layout, while managing the power/led/usb cables in between the two fans to the backpanel but it was a very tight fit. You can move the power panel to top bottom or rear if you have the space. My Thermaltake Smart 700W PSU blocked the bottom though. While the top was blocked the height and size of the Thermalright Phantom Spirit 120 SE Black CPU Cooler. And the rear was blocked by case fan and no real access for cable management through to the back panel. So I had to make the front faced orientation to work, which it did. All in all I am happy with the value of the product.
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Reviewed in the United States on November 17, 2025 by Matt
Style: Q300L V1
Color: Black
I love this case. I hate this case. Such wonderful and hateful things to say about the same case. Lets review. The good: This case is pretty. I love the aesthetics of this case. It's also very compact. It looks like a midget compared to my old Coolermaster HAF 900 series case. That's nice, since I get a lot more room on my desk, and I can position this tower in places I couldn't fit my old one. It's allowed me to do some really cool things with my desk setup that I couldn't do before. The dust covers are pretty, and they make it much easier to clean the case more frequently. (You'll still need deep cleaning every once and a while.) The bad: Boy oh boy does it suck to install things in this case. Like, cable routing is a FREAKING NIGHTMARE. If you don't care about that stuff, then it's still going to suck working in this case. "Cheap crap" is a nice description of everything about this case. The window? Cheap plexiglass that scratches easily. The PCI-E holes at the back of the case require you to pull them off using excessive force, potentially risking bending the thin metal between the slots. I ended up bending the back PCI-E screw pannel by overtightening the screws. Airflow? Gamer's Nexus tested the Q500L version of the case, and it was literally the worst case they ever tested for air flow. It caused components to thermal throttle (read: slow your computer down) at even low workloads. The Q300L is better, but it's still not winning any competitions. NEVER buy the Q500L. That seems like a long list of negatives, and it is. But I haven't gotten to the worst sin this case commits: Cable routing. I'm sure this is better than some other cases out there, but it's still pretty bad. Let's enumerate the problems you'll likely run into when routing cables: The movable button panel doesn't stretch long enough to route in convenient locations. The only place to run cables to the top of the case is a small hole that doesn't fit a standard power connector without causing you crazy amounts of grief and bending the plastic connectors while tearing chunks of flesh off your finger as you pull it through. There's not enough room on the back of the case to run your standard SATA cables for SSDs, and installing front fans means you lose out on a lot of potential cabling options. (You HAVE to move the button panel to the bottom/top if you use front fans) Why did I get this? I couldn't find a reasonably priced small sized case to put a Threadripper build in. I could have sprung for one of the smaller cases designed for compact builds, but each one of them had a deal-breaking problem. (Out of stock, couldn't fit micro-atx mobo, costs like 400$, etc.) I knew what I'd suffer through to get all the hardware to fit inside this case, while running custom cables for aesthetics. I consider it a worthwhile purchase. I spent several extra hours building this when compared with a case that was well designed. I ran into like 20 different configurations where things barely didn't fit by a millimeter or less, and the current configuration fits because I spent like 3 extra hours cabling this monster. But it was cheap, pretty, and small, so I'd probably do it again. Probably not the right case for you. Overall: This is a cheap case. It's an affordable place to put your computer. Don't expect much more than that. You can spend like 20$ more to get something truly worth holding your components.
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Reviewed in the United States on July 14, 2019 Reviewed in the United States on July 14, 2019 by Alex
Style: Q300L V1
Color: Black
So first I'd like to state that this review is specifically for the Q300L model. Amazon does this annoying thing where they mix all the reviews of all the models together and I can't stand it so I'm just stating the model flat out. I just built my 10 year old nephew’s PC using this case and I have to say that I was very surprised at how much I loved building in this case. Originally I bought the Compucase HEC HX300 case for 30$ from Newegg and I was just frustrated at the lack of air flow from that case. It only had room for one fan which was the back exhaust and that's it. It didn't even have holes for the power supply's intake fan! It was my fault for not researching enough and buying something so cheap. Then I did a little research and came across this case. It is only 50$ but has everything I want. I've seen PC builders on youtube build with this case and they all had great things to say. So the first thing I like about this case is obviously how much airflow it allows. It's an interesting design because there are holes all over the top, all over the bottom, and all over the front and you can install 4 fans if you wanted to (2 up top, 2 in front, 2 in bottom) in addition to the included exhaust fan at the back making it support up to 5 fans! Now with all those holes you might be thinking this is going to be an ugly case but as you'll see in the pictures this is not the case (pun intended) and it has very sleek looking dust filters to cover the top, front, and it’s not obvious from the picture but it has a filter on the bottom as well. I was pleasantly surprised to see that the filter is magnetic which made removing them to install my fans a breeze (pun intended). I also imagine cleaning them when they get dirty will also be very simple. You can simple remove them and just rinse with water. One tip when installing fans is that since there’s air holes all over, they actually made a very small indentation around the holes that you should screw in your fans. These “guides” are hard to notice but if you look closely you’ll see them. They have space for 140mm and 120mm fans depending on whatever you want. Air is able to easily flow through the filter so my air flow issues were resolved! The case also looks very nice in my opinion. I have the black model just because that’s what my nephew wanted but in review videos I’ve seen, the white one looks very nice as well. Cable management at the back is pretty good too and the case comes with a lot of zip ties. The filters I mention above are also very aesthetically pleasing. The power button, 2 USB ports, headphone jack, and speaker jack are on the side which I don’t mind. The interesting thing is that this IO panel can be unscrewed and moved to the other side which is nice. The clear side panel is acrylic but it’s a 50$ case so it’s fine. It doesn’t look bad at all. There’s also room in the cable management area for a 3.5” hard drive and 2 SSD’s inside the main area which is very good. Overall the case was pretty simple to build in. It’s designed very well to maximize airflow while looking great. I think this is an excellent case especially for the price. If you’re in the market for a cheap but good PC case, then you my friends have stumbled on a cheap but GREAT PC case. I would highly recommend this case and am willing to do even more expensive builds with this case in the future. One final note I’ll add, I built my nephew’s pc with a Ryzen 5 1600 processor and RX 480 gpu reference model targeting 1080p gaming and the heat in my old case with that one exhaust fan was reaching around 87 degrees C. After I added two intake fans in the front and one exhaust fan in the top along with the back exhaust fan that comes with this case my temperatures went down into the mid 70’s while gaming which is great. If you want looks as well as functionality for a great price, go with this case.
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Reviewed in the United States on June 25, 2020 by Fa
Style: Q300L V1
Color: Black
Bought this pc case for my friends budget pc with a ryzen 5 5500 and an rx 7600 and it looks beautiful. Some thing though. 1. Cable management is harder. There is limited space in the back so cable management is hard, but this is true for many cases. Not crazy hard but there isn’t a ton of room 2. Make sure to take out the GPU brackets before installing the motherboard. We didn’t do it and almost broke the motherboard, that is our fault though. Overall a very good budget case and fits well in desk, I’d recommend a semi modular or modular psu so cables are everywhere. Also it’s micro atx, and the front supports dual 140mm fans. Overall very nice case.
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Reviewed in the United States on March 6, 2026 by Jennifer Naponelli
Style: Q300L V1
Color: Black
I just built a PC for my daughter using this case, and as long as you're not going overboard with components, there's plenty of room. We used an mATX motherboard, and the case comes with a single 80mm fan in the rear. There's easily space for three more 120mm fans — possibly four, depending on your motherboard clearances. Airflow seems perfectly adequate, and the included dust screens are a nice touch. The motherboard tray is well-designed, with several pass-throughs in the corners and bottom. We routed all the cables behind the tray and back through to the motherboard, which made for a very clean build. RGB fans shine through well — lighting visibility is decent. This is a great budget case, but keep in mind that at this price point, the metal is thin. Don’t drop it or lean on it too hard — it can bend out of shape easily. I know some people knock the lexan panel, but if you keep your hands off it and use a microfiber cloth to clean it, you’ll be fine. Just avoid anything abrasive or it will scratch. We did run into a minor issue where the power button didn’t work initially — flipping the header on the motherboard resolved it. One other small gripe: the USB ports on the side panel are too close to the power button. If you plug in a USB stick near the power button, it’s very easy to accidentally shut off the PC — I did this a few times. Despite those quirks, there’s not much to complain about at this price. It’s a nice little case with good functionality and solid value.
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Reviewed in the United States on July 7, 2025 by P. Wells
Style: Q300L V1
Color: Black
Overall great! Major and unforgivable problem: the covers for PCI cards are soldered on the case and very hard to remove especially if the motherboard is already installed. I have to almost break the case to detach it to install a PCI network card
Reviewed in the United States on June 7, 2026 by Yang Xia
Style: Q300L V1
Color: Black
When I was picking my parts, I wanted to spend as little as possible on a case without going into the ultra budget rosewills and what not. Pretty much every case I was interested in was either in the $60 range or the $100+ range. I was going to settle on the thermaltake v21 and replace all the sides with windows, then I was going to settle on the fancy version of the q300l. I kept researching and researching and it sounds like cooler master fans aren't that great so getting two rgb ones with the fancy version sounded like a good deal but I had found plenty of cheap 6 packs of rgb fans and would prefer if all matched. This case at below $40 was just simply the most unique one at this price range and I had already decided on all the other parts (don't pick the case first) and tried imagining the build. I changed my mind on getting ring style fans, the perforated nature of this case would completely ruin the rings' lighting thru the walls, so the other option was fully lighted fans. Definitely the right choice in this one. You need to be careful with CPU coolers too, several popular ones are too tall by less than a mm. Just happens that the fans I got, uphere's (I took a chance and they are so good, don't let the brand scare you) also come on uphere's cooler and it fits PERFECT. No touching the side panel or anything. I didn't realize how black the case was as well and that is such a good thing. It is black, not grey. Cable management was as easy as can be with zip ties and fabric ties. Plenty of space to feed any cable heads thru any open route, I never got frustrated or had a problem making it look how I wanted. There's mixed info on the cooling performance. Lots of holes=lots of air. Gamers Nexus proved that false but I have yet to see temps over 75c during all benchmarks. Probably due to 9 fans. It just looks clean. I don't know if you can tell from the pictures. Cons: it's a cheap case so it's got more of a bare bones metal look than a sleek spaceship look. Not necessarily a bad thing. I really can't think of anything else, it was a complete joy to build in and everyone who's seen it really appreciates it. Would definitely recommend for budget builds and high end ones and is a perfect choice for custom builds built in quantity for offices and such at such a cheap price. Don't hesitate, if you think this case looks good even a little bit, it looks better in person and you shouldn't be disappointed. Make sure you are using micro atx motherboard. Just saying. Some people. Normal atx psu fits with a recessed bracket, thought it was weird but now I actually like it. It allows the power cable to bend at the edge of the case as opposed to sticking out and inch or so. Definitely a buy for those on a budget.
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Reviewed in the United States on May 28, 2019 Reviewed in the United States on May 28, 2019 by Bubba Grimm