Measure at waistline.
Measure from the small of your back, sloping downward to a point 3"- 4" below your navel.
If you are in-between sizes, either size will fit. However, most folks size down to avoid having to contend with greater fabric overlap in the front and a longer secondary strap. If your weight fluctuates up and down, it's better to size up.
If worn under clothing, the lumbar pad adds about 1.5 inches to your waist measurement, so if your regular pants are “just the right size,” the pants may not close while wearing Back-A-Line underneath.
There are 2 ways to wear the belt, depending on body type.
Fasten the belt snugly. You should feel firm pressure from the lumbar pad against your spine. If you suffer from some belly fat, lift your belly when you fasten the belt so that the belt can lift and support your belly weight.
Back-A-Line belts were originally designed for male anatomy and reliably fit most men. The belt can also be used by women with a straight or stocky build. Back-A-Line belts do not fit curvy or "pear-shape" women. (We're working on a solution!)
Those with spinal anomalies may not be able to use the belt. The Back-A-Line anatomic lumbar pad trains your back to assume a neutral lumbar lordosis. In order to be effective, your spine must be flexible enough to shape itself to the lumbar pad. If your spinal is inflexible or has a structural deformity, the Back-A-Line belt may be uncomfortable and ineffective. There is no harm in trying. It cannot hurt you. The worst thing that can happen is that it may not help.
Unlike elastic belts, which disable core muscles and cause atrophy (rather than a solution), Back-A-Line activates abdominal and spinal muscles which is a good thing for your body. It can be worn 24/7 if desired. We suggest you wear it all-day for the first few days to relieve pain and begin forming your new postural habits. Remember, it can take 3 weeks or longer to acquire sufficient muscle memory to establish new postural habits, so the more you wear the belt during this training period the better. If all-day is not feasible, wear it as much as you can. Your spine will tell you when you can reduce your time in the belt.
Remember: Back belts do not assure safe movements. They only promote them when used properly. Only you can guarantee back safety.
If you are not sure of the fit, remember that Back-A-Line offers a 30-Day Satisfaction Guarantee. So go ahead and give it a try!