15.6 vs 17.3 Inch Laptop Backpack: Which Size Do You Actually Need?

If you’ve ever shopped for a laptop backpack, you’ve seen the numbers: 13-inch, 14-inch, 15.6-inch, 17.3-inch. And if you’re carrying anything larger than a standard ultrabook, you’ve probably wondered whether a 15.6-inch bag will actually fit your machine — or whether you need to step up to a 17.3-inch backpack.

Here’s the problem: most buying guides don’t explain what those numbers actually mean. They tell you “15.6-inch laptops fit in 15.6-inch bags,” which is technically true but practically useless when every laptop has different bezels, thickness, and chassis dimensions.

This guide breaks down the real differences between 15.6-inch and 17.3-inch laptop backpacks — dimensions, weight, protection, and who each size is actually for. By the end, you’ll know exactly which one fits your laptop and your life.

The Most Important Thing to Understand: Diagonal ≠ Footprint

Before we compare the two sizes, we need to clear up the biggest source of confusion.

Laptop screen sizes are measured diagonally — corner to corner across the display, not including the bezel. That number tells you how big the screen is. It does not tell you how big the laptop actually is.

A 15.6-inch laptop typically has a chassis of approximately 36 × 24 cm (roughly 14.2 × 9.4 inches). A 17.3-inch laptop typically has a chassis of approximately 40 × 28 cm (roughly 15.7 × 11 inches).

That difference — about 4 cm in width and 4 cm in depth — might not sound like much. But when a laptop compartment is sewn to a specific size, 4 cm is the difference between “slides in easily” and “doesn’t fit at all.”

This is why the number on the backpack label matters. A backpack listed as “15.6-inch” is sized for a laptop with a footprint of roughly 36 × 24 cm. A backpack listed as “17.3-inch” is sized for a footprint of roughly 40 × 28 cm.

The takeaway: Don’t rely on screen size alone. Measure your laptop’s actual chassis (width, depth, and thickness) before you buy any backpack.

15.6-Inch Laptop Backpack: The Standard Choice

What It Fits

A 15.6-inch backpack is designed for the most common laptop size on the market. It comfortably accommodates:

• 15.6-inch laptops (the standard size for most business and general-purpose machines)

• 15-inch laptops (slightly smaller chassis, fits with a little room to spare)

• 14-inch laptops (fits loosely — you may want extra padding or a sleeve)

• 13-inch laptops (will fit but will move around; not ideal without a secondary sleeve)

• MacBook Pro 16 (2021–present) — chassis ≈ 35.57 × 24.81 cm; fits most 15.6-inch compartments, but check that the internal depth is at least 25 cm.
• MacBook Air 15 — chassis ≈ 34.04 × 23.76 cm; fits comfortably.
• MacBook Pro 14 — chassis ≈ 31.26 × 22.12 cm; fits with room to spare.

If you’re carrying a standard work or school laptop — a Dell XPS 15, a Lenovo ThinkPad, a MacBook Pro 15 — a 15.6-inch backpack is the natural fit.

Dimensions and Weight

A 15.6-inch laptop backpack typically has exterior dimensions of around 43 × 30 × 18 cm (about 17 × 11.8 × 7.1 inches). The internal laptop compartment is usually sized to fit a chassis of roughly 36 × 24 cm with a few centimeters of clearance for cables and accessories.

Empty weight varies by material and construction, but most 15.6-inch backpacks weigh between 0.7 kg and 1.5 kg (roughly 1.5 to 3.3 pounds). The lighter end of that range is achieved with lightweight nylon or polyester; the heavier end typically means more padding, reinforced stitching, and heavier-duty hardware.

The Trade-Off

Advantage: A 15.6-inch backpack is lighter, more compact, and more proportionate for daily commuting. It doesn’t look or feel like you’re carrying a suitcase on your back.

Limitation: If you have a 17.3-inch laptop, it will not fit. And if you’re carrying a 15.6-inch laptop inside a larger case or sleeve, the combined footprint may exceed the compartment dimensions.

17.3-Inch Laptop Backpack: The Large-Format Option

What It Fits

A 17.3-inch backpack is designed for the largest standard laptop category. It accommodates:

• 17.3-inch laptops (gaming laptops, mobile workstations, desktop replacements)

• 17-inch laptops (fits comfortably)

• 16-inch laptops (fits with room to spare)

• 15.6-inch laptops (fits — but the backpack will be larger than necessary)

If you’re carrying a gaming laptop, a mobile workstation (like a Dell Precision or HP ZBook), or any 17-inch machine, a 17.3-inch backpack is what you need.

Dimensions and Weight

A 17.3-inch laptop backpack typically has exterior dimensions of around 48 × 34 × 22 cm (about 18.9 × 13.4 × 8.7 inches). The internal laptop compartment is sized for a chassis of roughly 40 × 28 cm with clearance.

Empty weight varies more widely than the 15.6-inch category because 17.3-inch backpacks tend to be built with heavier-duty materials and more reinforcement. A typical 17.3-inch backpack weighs between 0.8 kg and 2.8 kg (roughly 1.8 to 6.2 pounds). The lighter models use streamlined designs with minimal padding; the heavier models include extensive organization panels, reinforced bases, and premium hardware.

The Trade-Off

Advantage: A 17.3-inch backpack fits the largest laptops on the market without squeezing or stressing the zippers. If you need to carry a 17-inch machine, this is your only real option.

Limitation: It’s larger, heavier, and bulkier. A 17.3-inch backpack takes up more space on public transit, looks more like luggage than a daily carry, and adds noticeable weight even when empty.

Side-by-Side Comparison