Backpacks aren’t one-size-fits-all, and this guide explains standard backpack sizing and how to adjust a pack to fit you comfortably.
Key Takeaways
- A standard everyday backpack holds about 20 to 30 liters, which is a typical size for school packs.
- Measure your torso length first so you can choose a backpack that fits your body.
- Adjust the shoulder straps, hip belt, load lifters, and sternum strap so that most of the weight rests on your hips.
If you’ve ever worn a pack that felt awkward or left you with sore muscles, it probably wasn’t the right fit for your body. The wrong backpack size can put extra strain on your back, shoulders, and hips, even if you wear it for short trips. Taking the time to choose the right size helps you stay comfortable and protects your body over time.
Are Backpack Sizes All the Same?
No, backpack sizes are not all the same. Packs come in different shapes and sizes, so there isn’t a one-size backpack that works for everyone. Many brands offer multiple sizes or adjustable fittings because people have different torso lengths and builds.
What Is a Standard-Size Backpack?
A standard-size backpack is typically a medium everyday pack of about 20 to 30 liters in capacity. It’s basically the typical youth size for school backpacks that are around 18 to 20 inches tall and 12 to 14 inches wide. Because it can be adjusted, this size typically works well for adults and school students.
How Do You Size a Backpack To Fit Properly?
Sizing a backpack properly means adjusting it to your body so it feels comfortable and balanced.
Measure Your Torso Length
Your torso length is the key measurement for a properly fitting backpack. To find it, have a friend help you with a cloth measuring tape. Tilt your head forward and find the bony bump where your neck meets your shoulders. That’s your 7th cervical vertebra (C7), which marks the top of your torso.
Next, place your hands on the top of your hip bones (the iliac crest) on both sides and imagine a line straight across your lower back at that point. Measure the distance from the C7 neck bump straight down your spine to that imaginary line at your hip bones. This distance is your torso length.
Choose the Correct Backpack Size
Now use your torso length to find which backpack size category you fall into. Backpack brands usually provide size charts that match torso length ranges to pack sizes (small, medium, large).
For example, a torso length of about 18–19 inches would typically put you in a “Medium” pack size for many brands. If your measurement is on the border between sizes, check the manufacturer’s chart. One brand’s medium might overlap with another’s large.
Always refer to the specific pack’s sizing guide. The goal is to pick a backpack size that matches your torso measurement as closely as possible.
Adjust the Shoulder Straps
Once you have the correct size, put the backpack on and tighten the shoulder straps. To tighten them, pull down and back on the ends of the shoulder straps until they wrap comfortably around your shoulders. The shoulder straps should be snug but not bearing most of the weight. In other words, your shoulders shouldn’t feel a heavy load because your hips will actually carry the weight.
Check the strap attachment points on the pack. The place where the shoulder straps attach should sit about 1 to 2 inches below the tops of your shoulders (around the height of your shoulder blades). If those anchor points are way above or below your shoulders, it may mean the pack’s torso length isn’t adjusted correctly, or you picked the wrong size backpack.
When the shoulder straps are correctly adjusted, they hold the pack close to your body without gapping, but you should feel relief once you properly engage the hip belt to take the weight. You can always fine-tune the shoulder strap tension by slightly loosening or tightening as needed to relieve any pressure points during use.
Position and Tighten the Hip Belt
The hip belt is the most important strap for carrying weight, so adjust it before the other load-bearing straps. Buckle the hip belt and position it so that the padded sections of the belt sit on top of your hip bones (the iliac crest). In other words, the belt should “hug” the upper ridge of your hips.
If the belt padding is too high (above your hips) or too low (sliding over your butt), readjust by tightening or loosening the shoulder straps to raise or lower the pack until the belt is in the correct spot.
Once positioned, tighten the hip belt strap until it’s snug around your hips. Check that the padded portions of the belt extend slightly past the front of your hip bones for proper support. If there’s too much gap or you can’t get it tight enough, the belt might be the wrong size for you. But generally, a well-fitted hip belt will feel comfortable and take the load off your shoulders.
Fine-Tune the Load Lifters
Load lifter straps are the small, angled straps connecting the top of the shoulder straps to the top of the pack. After the hip belt and shoulder straps are set, adjust these load lifters. Gently pull them until you feel them start to draw the top of the pack toward your shoulders. They should form roughly a 45-degree angle between your shoulder straps and the backpack body.
The purpose of load lifters is to prevent the top of the pack from pulling backward and to help transfer some weight to your front, balancing the load. Do not overtighten the load lifter straps. If you crank them too tight, you can actually lift the shoulder straps off your shoulders and cause pressure or pinching at the front of your shoulders.
The pack shouldn’t be leaning away from you, but you also shouldn’t feel the straps digging in. A good sign of proper load lifter adjustment is that there’s no gap between your shoulders and the shoulder straps, and the pack feels close to your upper body. If you notice a gap at the shoulder or discomfort, try loosening the load lifters slightly until it feels right.
Adjust the Sternum Strap
The sternum strap is the small strap across your chest that connects the shoulder straps. If your backpack has one, slide the sternum strap so it sits about an inch below your collarbones.
Buckle the sternum strap and gently tighten it to keep the shoulder straps in place and prevent slipping. The strap should feel secure but not tight. If the sternum strap is overtightened, it can affect the fit or make breathing uncomfortable, so leave enough room for natural movement and easy breathing.
Load the Backpack and Reassess the Fit
Test the pack’s fit with some weight. Add about 10 to 15 pounds to the backpack, put it on, and readjust as needed.
Walk around and notice how the weight feels. The pack should feel balanced and close to your back. If the pack still feels off, you may need a different backpack size and should remeasure your torso to see if you made a mistake from the beginning.
Backpack Sizing Is Easier for Your Customers With the Right Shopify App
If you’re using Shopify to sell backpacks or other apparel, you need the Kiwi Sizing app. When customers aren’t sure which size to choose, they hesitate or guess, which often leads to more returns.
With Kiwi Sizing, you can give shoppers clear size charts, helpful guides, and personalized fit recommendations that make choosing the right backpack size easier. You can show multiple size tables, images, or videos right on the product page so customers feel confident before they buy. You can even set up size guides that apply automatically to entire collections, which saves you time as your store grows.
If you want fewer returns and more confident buyers, a Shopify size chart app like Kiwi Sizing gives your store the polished sizing experience customers expect and helps them pick the right apparel every time.
