This will be a brief exploration in how to properly size & fit a motorcycle jacket; focusing on getting the measurements, body types, how design effects fit, and how to confirm fit.
Ideally motorcycle clothing should fit snug; which serves to prevent fabric flapping, avoid excess material bunching uncomfortably in the riding position.
And in an unexpected get-off; snug fit keeps armor and/or abrasion resistant sections in the correct place. It also reduces chance for skin-shear (layers of skin separating from each other) and friction burns (70+mph rug-burn anyone?) from the material and your skin sliding over each other under pressure at different rates.
Key measurements:
- Shoulder Width should be measured across the back from shoulder edge to shoulder edge, tracking the natural curve of your back.
- Sleeve Length will be measured from the top of the shoulder (around where arm seams typically start) down the arm to the wrist while your arm/shoulders are relaxed.
- Chest Circumference would be measured around the chest, under the armpits at your chest's widest point with your chest relaxed.
- Stomach Circumference will be taken around the stomach inline with your bellybutton while the stomach is relaxed.
- Waist Circumference is measured around your natural waist (3-4 fingers below your bellybutton and right above the hip joint). For women's clothing Waist can mean the 'high waist' (stomach circumference) as opposed to the 'natural waist', so double-check which it is.
Body Shape factors
- Broad Shoulders - If you aren't sure if you have them, divide your shoulder width by chest circumference. Should that result be greater than 0.45, e.g. 19" / 40" = 0.475, your shoulders are broader than typical. When you find yourself near the top of a size range for chest without a shoulder width listed in the chart, you may need to size up or risk dislocating a shoulder getting in/out of the jacket.
- Muscular Arms & Back - If you carry more bulk around biceps, triceps, etc. than most, then you might find pinching under the arm or constriction in the sleeve. If you are in between sizes, definitely consider sizing up.
- Long or Short Torso - The typical torso range is between 15-22" (38-56cm); where women tend toward the shorter end (~16"), and men tend toward the longer end (~18"). If you are more than 2" (5cm) either side of those gender averages you may have a challenge finding a good fit. Sizing up or down doesn't necessarily always address that, as some manufactures have a single standard length across sizes.
Style of Cut
Depending on the primary market for the jacket, sizing and cut can very greatly.
Typically American cuts have larger arm holes and are straight or flare slightly toward the waist, and a measurement like a 32" waist can have up to an extra 0.25-0.33" (6-9mm) of room depending on the maker.
While European cuts tend to be more tapered toward the waist and have narrower arm holes, plus they may only have 2-4mm (0.08-0.16") of wiggle room from the base measurement.
Jackets with armor included will generally factor the armor present in the fit, while one with only pockets for armor may not as they can't be sure what armor you'll use. The type of armor also effects flexibility in joints they cover, so if you're planning to add a stiffer or thicker armor you may need extra wiggle room.
Likewise if you foresee layering under the jacket at some point, account for that in your measurement to ensure it still fits when you wear your favorite flannel, hoodie, etc. under it.
Check the Size Chart
Even if you think you know your size, check the size charts to verify your expectation vs. measurements are available in the chart. Occasionally some manufactures can throw curve-balls, such as seam to seam measurement where you expected a body measurement or width instead of circumference.
Ideally you should match the measurement methodology listed in the the chart, but if you have to make an estimate be sure err to the side of assuming it will fit tighter than expected.
Check the Fit
After putting on the jacket for the first time with everything fastened, strike a riding position; e.g. sit with your elbows out and arms forward like you're grasping your handle bars or clip-ons.
In this position the jacket should feel fairly snug like a warm embrace, yet neutral without any obvious pinching, bunching, or breathing restriction. Try turning your shoulders to look behind yourself to the right and left. If you find it's feels too tight around the body to allow you do that, size up. If you have material that is bunching and poking into you as you move, size down.
Try to lift your arms over up over your head, if you can't or when you do it exposes your lower back or the cuff rides up your forearm past the wrist bones. Then you may need a bigger size or a longer length to avoid gaps in coverage if you went prone during a slide.
Now look straight-up and straight-down as well as over your left and right shoulders to check for anything that would impede normal head/neck movements.
Before you go out riding for the first time with the jacket try gearing up as you would normally, repeat the previous checks, and then reverse the process to take off your gear. You may find certain combinations of gear change how you move and how comfortable you feel.
Likewise, you may just find certain gear is more difficult to put on or take off while wearing the jacket. Which is better to know now before it's been exposed to the elements as most stores, including ours, will not accept returns on jackets that you've ridden in.