How to Size an Ultralight Frame Pack for Your Torso
By Zpacks | Level Up Your Next Adventure | Published: 2026-10-22
Category: How-to Guides
Learn to measure your torso and choose the right frame pack size. Get step-by-step guidance for a comfortable, efficient fit for your next adventure.
Quick answer
To size an ultralight frame pack, measure your torso length and hip circumference, then use the pack's sizing chart—like the Arc Haul Ultra's adjustable torso range—to find your fit.
Why torso length matters more than height
Your torso length determines how the pack's frame transfers weight to your hips. A pack that's too long will ride low and strain your shoulders; too short and the hip belt won't sit on your iliac crest, reducing stability.
Frame packs like the Arc Haul Ultra are designed with adjustable torso ranges, so you can fine-tune the fit as you move or if your measurements change. For example, the Women's Arc Haul Ultra 60L fits torsos around 16–19 inches, while the unisex versions offer a broader range.
Women-specific fit considerations
Women and teenagers with a smaller build often need a pack with shorter, slimmer shoulder straps to avoid gaping at the shoulders. The Women's Arc Haul Ultra 60L is built with these features, and its torso height can be adjusted upward as a young adult grows—making it a versatile choice for growing hikers.
If you're between sizes, choose the smaller torso range and use the adjustment system to fine-tune. A pack that's slightly short can be extended, but one that's too long can't be shortened.
How to measure your torso and size your pack
- Find your C7 vertebra: Tilt your head forward and feel for the bony bump at the base of your neck. This is your C7 vertebra. Mark it with a small sticker or have a friend note the spot. Common mistake: measuring from the wrong vertebra. Use the most prominent bone when you tilt your head.
- Measure to your iliac crest: Place your hands on your hips with thumbs pointing back. The top of your thumbs rests on your iliac crest—the top of your hip bones. Have someone measure from the C7 mark straight down to that line. Checkpoint: Keep the tape straight and level; a curved measurement adds inches.
- Record your torso length: Write down the measurement in inches or centimeters. This number is your torso length, which you'll compare to the pack's sizing chart. Common mistake: measuring over bulky clothing. Do this in a thin shirt for accuracy.
- Check the pack's torso range: Look at the pack's specifications for the adjustable torso range. For example, the Women's Arc Haul Ultra 60L fits 16–19 inches, while the unisex versions cover a broader range. If your torso falls within the range, the pack can be adjusted to fit. Checkpoint: If you're at the edge of a range, try the next size up or down to compare.
- Measure your hip circumference: Wrap a tape measure around your hips at the iliac crest, where the hip belt will sit. Compare this to the pack's belt size options—many packs, like the Arc Haul Ultra, offer multiple belt lengths. Common mistake: measuring at your natural waist. The belt rides on your hip bones, not your waist.
- Adjust and test the fit: Once you have the pack, set the torso length to your measurement and put it on. Load it with weight and adjust the hip belt so it sits snugly on your iliac crest. The shoulder straps should wrap your shoulders without gaping, and the load should feel carried by your hips. Checkpoint: Walk around and bend slightly. If the pack shifts or pulls, readjust the torso length or belt.
Products mentioned in this guide
- Women's Arc Haul Ultra 60L Backpack: The Women's Arc Haul Ultra 60L is sized for women and teenagers with a smaller build, with shorter, slimmer shoulder straps and a torso range of 16–19 inches. This pack provides a tailored fit for narrower shoulders and can grow with a young hiker, making it a smart choice for women and teens.
Women's Arc Haul Ultra 60L Backpack - Arc Haul Ultra 60L Backpack: The Arc Haul Ultra 60L features an adjustable torso height and is made from Ultra 100X material for durability on long resupply stretches. The adjustable torso lets you dial in the fit for your exact torso length, while the durable fabric handles rugged trails like the Appalachian Trail.
Arc Haul Ultra 60L Backpack - Arc Haul Ultra 50L Backpack: The Arc Haul Ultra 50L offers the same adjustable torso system and Ultra 100X construction in a slightly smaller volume. If you prefer a lighter, more compact pack for shorter trips, the 50L gives you the same fit customization with less capacity.
