Michael Turner
Use a soft, flexible tape; mark the most prominent cervical vertebra (C7) and the highest points of the iliac crests (top of pelvis), take the distance along the back contour and match that number to the manufacturer’s frame-size chart to pick the right pack.
Standard categories: Short – 38–43 cm (15–17 in); Medium – 43–48 cm (17–19 in); Long – 48–53 cm (19–21 in). If the recorded value lands between sizes, choose the longer option when hauling loads above 20 kg; choose the shorter option when typical baseweight remains under ~10 kg.
Technique: stand relaxed with a neutral spine and level gaze; remove bulky outer layers. To locate C7, drop the chin and feel for the most prominent neck bone. To find the iliac crests, place hands on hips and note where fingertips rest. Run the tape along the curvature of the back rather than a straight line across the shoulders; aim for accuracy within ±1 cm.
Fit checks after selection: the hipbelt must sit squarely on the iliac crests and transfer load to hips; shoulder straps should wrap around shoulders without digging into the trapezius when loaded; adjust the frame’s vertical adjusters and load lifters according to the manufacturer’s instructions. Women’s-specific models often shift recommended span by about 1–2 cm and include narrower shoulder geometry; compare those specs when applicable.
Identify the C7 vertebra (upper-back landmark)
Press the base of the neck and tilt the head forward; the most prominent, single-tipped bony bump felt in the midline is C7.
Place the pads of your index and middle fingers at the occiput and slide downward along the spine until you meet the first distinct spinous process that projects noticeably – that position corresponds to C7 (the seventh cervical vertebra).
Ask the person to tuck their chin toward the chest while you palpate: C7 usually becomes more pronounced with neck flexion. Use steady, moderate pressure and small upward–downward glides to confirm the contour rather than broad sweeping motions.
To distinguish C7 from the first thoracic level, palpate one level below; T1 often sits less prominent and aligns more with the slope of the upper back. In individuals with short necks or thick soft tissue, have them lift the shoulders slightly and repeat the chin-tuck to improve palpability.
| Step | Action | Expected finding |
|---|---|---|
| 1 | Sit upright; relax the neck. | Neutral posture allows clearer landmarks. |
| 2 | Palpate midline from occiput downward with two fingers. | Feel sequential spinous processes until the first pronounced bump. |
| 3 | Have the person tuck chin; re-palpate. | C7 should become more noticeable compared with adjacent levels. |
| 4 | Verify by locating the next lower process (T1) and comparing size. | T1 is usually smaller and less protruding than C7. |
Locate the top of the iliac crest (hip bone) on your side
Stand upright with feet shoulder-width apart and place the flat of one hand on the lateral pelvis, fingers angled toward the spine.
Slide fingertips along the curved ridge running from the anterior superior iliac spine (ASIS) to the posterior superior iliac spine (PSIS) and identify the highest palpable lateral point – the iliac crest apex.
Technique
Keep muscles relaxed; inhale normally and let hips settle so the bony ridge becomes more prominent. Use the pads of three fingers together and press gently, then increase pressure until you feel a firm, slightly rounded edge rather than soft tissue.
If visibility is needed, use a hand mirror or ask someone to mark a small dot with a washable pen at the apex. When marking alone, touch the spot with one fingertip, then transfer the finger position to a mirror-held marker to avoid shifting.
Adjustments by body habitus
Lean slightly to the opposite side to tense the iliac crest on the side being examined; this tightens surrounding tissue and makes the ridge easier to detect. For thicker soft tissue, hook the fingertips under the ridge and rock anteriorly and posteriorly to distinguish bone from fat or muscle.
Confirm placement by tracing medially along the ridge until you encounter the PSIS dimples at the lower back; a consistent bony curve between ASIS and PSIS verifies the correct apex location.
Prepare posture and tools: standing position and tape placement
Stand barefoot, feet shoulder-width apart, shoulders relaxed, gaze level; maintain neutral spine with knees slightly soft (≈5° bend).
- Flexible cloth tape, non-stretch, 150 cm / 60 in total, 1.5 cm / 0.6 in wide; avoid metal or retractable tapes.
- Fine-tip washable skin marker or small adhesive dot to mark points.
- Full-size mirror mounted at eye height or a helper to anchor the top end and steady the tape.
- Rigid ruler (30 cm / 12 in) and notebook to record readings immediately.
- Confirm the identified upper landmark and the hip crest are visible through clothing or mark each spot with a small dot.
- Secure the tape end at the upper landmark, keeping the tape centered on the midline. Hold the tape snugly against skin so it follows the natural curve without kinking.
- Extend the tape down the midline until it reaches the hip crest mark. Keep the tape flat and aligned with the spine; avoid crossing ribs, waistband, or clothing seams.
- Maintain relaxed posture during the entire action: inhale normally, relax shoulders, keep gaze straight ahead; avoid arching the lower back or tilting the pelvis.
- If alone, use the mirror to confirm the tape runs straight down the back. If assisted, have the helper steady both tape ends while you remain perfectly still.
- Where the tape meets the hip crest, transfer a mark to paper or read the tape against the ruler immediately to obtain a numeric reading.
- Permissible slack: under 5 mm; acceptable skin indentation: up to 2 mm. Excessive compression or looseness invalidates the reading.
- Repeat the procedure twice and use the average of two consistent readings separated by a short rest.
- If using a floor mat during setup, maintain hygiene by consulting how to clean cat litter mat.
C7–Iliac Crest Vertical Distance: Partner Method
With C7 and the top of the iliac crest already marked, have a partner align the zero of a non‑stretch tape at C7 and run it straight down alongside the spine to the crest apex; read where the tape crosses the marked hip point.
Partner technique: hold the tape taut without compressing skin, sight the tape at eye level to guarantee a vertical line, and use a free hand to steady the tape at midpoints so it does not twist or slip.
Repeat protocol: take three independent readings, repositioning the tape between each. If readings differ by more than 5 mm, repeat until two consecutive values fall within 5 mm. Record the arithmetic mean rounded to the nearest 5 mm (0.5 cm).
Precision tips
Mark points with a washable pen; read at eye level; take the tape vertically rather than following spinal curvature; confirm the crest apex with gentle palpation while the person stands relaxed. Use a rigid ruler only to verify a questionable tape reading, not as the primary tool.
Reference ranges and interpretation
Quick reference (approximate): Short: <41 cm (<16 in); Medium: 41–48 cm (16–19 in); Long: 48–53 cm (19–21 in); X‑Long: >53 cm (>21 in). If the average falls on a boundary, choose the smaller frame setting for a closer fit.
Common errors: slouching, tape placed diagonally, tape compressing soft tissue, or mislocated crest point. Correct by standing neutral, partner sighting the tape, re‑marking the crest while standing, then retaking readings. If not using a framed carry, consider alternative luggage: best most convenient travel duffel bags.
Adjust Sizing When Wearing Heavy Layers and with Spinal Curvature
Add 1–3 inches (2.5–7.5 cm) to a baseline figure when wearing bulky outerwear: thin fleece +0.5–1 in (1.3–2.5 cm), down jacket +1–2 in (2.5–5 cm), expedition parka or layered mountaineering kit +2–3 in (5–7.5 cm).
Thoracic kyphosis: increase harness rise by 0.5–1.5 in (1.3–3.8 cm) relative to baseline and use a slightly longer shoulder strap setting so straps sit on the deltoid rather than the neck. Lumbar lordosis: decrease rise by 0.5–1 in (1.3–2.5 cm) to prevent the hip belt from riding too low. For mixed curvature, split the difference and validate with a loaded trial.
Scoliosis or asymmetric posture: pad the low side of the hip belt with 5–10 mm foam, shift sternum strap up or down up to 2 in (5 cm) to balance tension, and consider a custom-molded hip belt if asymmetry exceeds 3–4 cm. When making unilateral strap adjustments, keep load distribution target at roughly 70–80% on the pelvis and 20–30% on the shoulders.
Field verification routine: don full kit, tighten hip belt on iliac crest, set shoulder straps until gap at the lumbar region is 1–2 finger widths (approx 1–3 cm), walk 10–15 minutes on varied grade, then tweak in ±0.5 in (±1.3 cm) steps. Mark final strap ladder position with tape or a permanent marker to replicate fit quickly.
If travel includes maritime segments, check compatible luggage and carry solutions: best luggage for sailing trip
Match spine-span to pack sizing charts and try-on tips
Compare the C7–iliac value obtained earlier to manufacturer size charts and select the size whose range includes your number; if on a boundary, try both adjacent sizes before deciding.
Typical chart ranges (guideline): Small: ≤40 cm (≤15.5″); Medium: 41–46 cm (16–18″); Large: 47–51 cm (18.5–20″); X‑Large: ≥52 cm (≥20.5″). Cross-check both cm and inches since brands differ by 1–2 cm.
Load the pack to a realistic weight: day trips 8–12 kg (18–26 lb); overnight 12–20 kg (26–44 lb); extended loads 20–30 kg (44–66 lb). Fasten the hipbelt over the iliac crest and tighten until the majority of weight sits on hips; then snug shoulder straps so shoulder straps contact the upper deltoid without digging. Set load lifters around 30–45° and place the sternum strap mid‑chest. Walk, climb stairs and simulate terrain for 10–15 minutes to confirm dynamic comfort.
If the model has an adjustable harness, confirm the adjustment range covers your C7–iliac value; note adjustment increments (typical 1–2 cm steps). Fixed harnesses that are shorter than your span will force the hipbelt too low; those that are longer will let the shoulder straps ride off the shoulder. When between sizes, prefer the larger size when expecting heavy loads and the smaller size when carrying consistently light loads or when micro‑adjust harness options exist.
Female‑specific designs usually feature narrower shoulder pitch and a more contoured hipbelt. Test these models even when unisex sizing appears to match chart numbers. Record the model, nominal size and specific harness/hipbelt settings that produced correct pack‑to‑body contact; take photos of strap alignment and hipbelt placement to compare during later purchases.
