One of the most common mistakes people make when purchasing a laptop bag is choosing the wrong size. A bag that is too small will not accommodate your laptop properly, potentially causing zipper strain and inadequate protection. A bag that is too large allows your laptop to shift during transport, which can lead to bumps against bag hardware and other items. Finding the perfect fit requires understanding how laptops and bags are measured, and knowing exactly what dimensions matter.
This guide will walk you through the process of measuring your laptop correctly and matching those measurements to bag specifications, ensuring you select a bag that fits your device perfectly.
Understanding How Laptops Are Measured
Laptop screen sizes are measured diagonally from one corner to the opposite corner, not including the bezel (the frame around the screen). This is the number you see in product names like "15.6-inch laptop" or "13-inch MacBook." However, this measurement tells you very little about the laptop's actual physical dimensions, which is what matters for bag selection.
Two laptops with identical screen sizes can have significantly different overall dimensions. A 15.6-inch gaming laptop with thick bezels and substantial cooling systems might measure 380mm wide and 30mm thick, while a 15.6-inch ultrabook with slim bezels could measure just 355mm wide and 17mm thick. This is why you cannot rely solely on screen size when choosing a laptop bag.
A "15-inch laptop bag" from one manufacturer might fit a 15.6-inch ultrabook perfectly but be too small for a 15-inch gaming laptop. Always check actual measurements rather than relying on screen size labels.
How to Measure Your Laptop
To find the right bag, you need three measurements from your laptop: width, depth, and height (thickness). Here is how to measure each accurately.
Width (the longest dimension)
Close your laptop and place it on a flat surface. Using a tape measure or ruler, measure from the left edge to the right edge at the widest point. This is typically across the front of the laptop where the palm rests. Record this measurement in millimetres for precision.
Depth (front to back)
Measure from the front edge (where the laptop opens) to the back edge (where ports and hinges are typically located). Take this measurement at the deepest point, as some laptops taper toward the front.
Height/Thickness
Measure the laptop while closed, from the bottom surface to the highest point on top. Include any rubber feet on the bottom, as these add to the overall height. Some laptops are wedge-shaped and thicker at the back; measure at the thickest point.
Account for Cases and Accessories
If you use a protective hardshell case, sleeve, or skin on your laptop, take measurements with these accessories attached. A hardshell case can add 3-5mm to each dimension, which can make the difference between fitting in a compartment and not fitting.
- Measure with laptop closed
- Record width, depth, and thickness in millimetres
- Include any protective cases or skins
- Measure at the widest/thickest points
- Double-check measurements before purchasing
Understanding Bag Compartment Specifications
Quality laptop bags list the internal dimensions of their laptop compartment. Look for these specifications rather than just the advertised laptop size compatibility. When comparing your laptop measurements to bag specifications, you want clearance on all sides.
Ideal Clearance
For width and depth, aim for 5-15mm of clearance on each side. This allows for easy insertion and removal while preventing excessive movement. For thickness, 3-10mm of clearance is typically sufficient, as padding will compress slightly when zipped.
Too Tight
If the compartment dimensions are very close to your laptop dimensions (less than 3mm clearance), insertion will be difficult, and you risk stressing zippers and seams every time you use the bag. Over time, this can cause premature wear and damage.
Too Loose
Compartments with more than 20mm of extra space allow your laptop to shift significantly during transport. This movement can result in your laptop banging against zippers, buckles, or other items in the bag, potentially causing scratches or damage.
Common Laptop Sizes and Typical Dimensions
While you should always measure your specific laptop, here are typical dimensions for common laptop categories to give you a general reference:
13-inch Ultrabooks: Approximately 300-310mm wide, 210-220mm deep, 14-18mm thick. Examples include 13-inch MacBook Air and Dell XPS 13.
14-inch Business Laptops: Approximately 320-330mm wide, 220-230mm deep, 16-20mm thick. Examples include ThinkPad X1 Carbon and HP EliteBook 840.
15-inch Mainstream Laptops: Approximately 355-365mm wide, 235-245mm deep, 18-24mm thick. This is the most common size category with significant variation between models.
16-inch Professional Laptops: Approximately 355-360mm wide, 245-255mm deep, 16-22mm thick. Examples include 16-inch MacBook Pro.
17-inch Desktop Replacements: Approximately 395-420mm wide, 270-290mm deep, 25-35mm thick. These large laptops require specially designed bags.
Special Considerations for Australian Buyers
When shopping for laptop bags in Australia, be aware that some international retailers list dimensions in inches while Australian retailers typically use centimetres or millimetres. Always convert to consistent units before comparing. Additionally, bag sizes marketed in one country may differ from the same brand's sizing in another market.
If purchasing from overseas retailers, confirm the exact internal compartment dimensions rather than relying on size labels. A "15-inch laptop bag" from a US retailer may have different actual dimensions than a "15-inch laptop bag" from an Australian retailer.
Be careful when comparing specifications: 15 inches ≈ 381mm ≈ 38.1cm. Mixing up units can lead to ordering a bag that is completely wrong for your laptop.
Beyond the Laptop: Considering Overall Bag Capacity
While the laptop compartment size is crucial, also consider what else you need to carry. A bag that perfectly fits your laptop but has no room for your charger, mouse, and documents is not practical. Think about your typical daily carry:
- Power adapter and cables: Laptop chargers, especially for gaming laptops, can be bulky. Ensure there is pocket space for these essentials.
- Documents: If you regularly carry A4 papers or folders, check whether the bag accommodates documents without folding.
- Personal items: Water bottle, lunch, phone, wallet—these everyday items need homes in your bag too.
- Additional tech: External drives, headphones, tablets, and mice all require dedicated space.
Many bags list total capacity in litres. For reference, a minimalist laptop-only bag might be 10-15 litres, while a fully-featured commuter bag ranges from 20-30 litres. Travel-oriented laptop bags can exceed 40 litres.
When to Size Up or Down
Sometimes choosing a bag slightly different from your exact laptop size makes sense:
Size up if: You plan to upgrade your laptop to a larger size soon, you want to add a protective sleeve inside the bag, or you regularly carry a tablet alongside your laptop.
Size down if: You prioritise a compact, lightweight carry, you never add additional cases to your laptop, or you want to minimise overall bag bulk.
Final Sizing Tips
Before making your purchase, verify all measurements one more time. If possible, try the bag in-store with your actual laptop. For online purchases, check the retailer's return policy in case the fit is not quite right.
Remember that padding thickness affects usable interior space. A bag with 15mm of padding on each side of the laptop compartment will have less internal width than its external dimensions suggest. Quality bag manufacturers account for this in their specifications, but it is worth checking whether listed dimensions are internal or external measurements.
Taking the time to measure correctly and match specifications carefully will ensure you find a laptop bag that protects your device properly, carries comfortably, and serves you well for years. For more guidance on bag features beyond sizing, check out our complete beginner's guide to laptop bags.