I have spent more nights than I can count waking up with a stiff neck and a headache that seems to radiate right up the back of my skull. For years I blamed my mattress, my sleeping position, even the weather. The real culprit, I eventually figured out, was something far simpler: my pillow. I had been using the same flat, beaten-down pillow for nearly a decade, because I thought all pillows were more or less the same. They are not. The difference between a good night and a bad one often comes down to one thing you never see on the packaging: loft.

Loft is the height of the pillow when it is resting under your head. It sounds trivial, but it changes everything about how your spine lines up during sleep. If your pillow is too low, your head drops forward and your neck bends at an awkward angle. If it is too high, your chin jams toward your chest and your upper back takes the strain. The right loft keeps your head, neck, and torso in a straight line, so your muscles can relax completely. I only realized this a few months ago when I switched to a pillow from bespillow, which lets me adjust the fill to match my body. That one change cut my morning aches by maybe 80 percent.

Most people never think about loft because the pillow industry does not make it easy. The standard product is a uniform blob of polyester or down, stuffed into a cover and sewn shut. You buy it, you fluff it, and you hope for the best. But a one-size-fits-all pillow simply cannot work for everyone. A tall person with broad shoulders needs a thicker pillow than a short person with narrow shoulders, because the distance from the edge of the mattress to the side of the neck is different. That distance is the actual number that matters, and you can measure it yourself in under two minutes.

How to Measure Your Own Loft Requirement

Lie on your side on a firm surface, like the floor or a bare mattress. Keep your head in a neutral position, as if you were standing up and looking straight ahead. Have someone measure the height from the top of your shoulder to the tip of your ear. That measurement is your ideal loft range, usually somewhere between 3 and 6 inches. If your pillow is significantly lower than that, you are sleeping with your neck bent sideways, which explains the morning pain. If it is higher, you are craning your head upward and creating a different kind of stress.

This method works for side sleepers, but back and stomach sleepers need different numbers. Back sleepers need a lower loft, generally 2 to 4 inches, because the neck curve is less extreme when you face upward. Stomach sleepers need the flattest pillow of all, often less than 2 inches, because any height forces the neck into rotation. The tricky part is that many people change positions during the night without knowing it. They fall asleep on their back, then roll to their side an hour later. A pillow that works for one position can cause problems in another, which is why adjustable loft options have become popular.

I tested this with a few friends who complained about sleep quality. One of them, a 6-foot-2 guy who sleeps on his side, was using a thin feather pillow that measured about 2 inches of loft after he flattened it. His measurement said he needed around 5.5 inches. He switched to a firmer, taller pillow and reported that his neck pain disappeared in about four days. Another friend, a 5-foot-3 woman who sleeps on her back, was using a thick memory foam pillow that propped her head up too far. She downsized and stopped waking up with a sore throat from the awkward angle. These are not scientific studies, but the pattern holds: people who match pillow loft to their body geometry see real improvements.

What to Look For in a Pillow Beyond Loft

Loft is the biggest factor, but it is not the only one. The fill material affects how the loft behaves over time. Polyester clumps and flattens quickly. Down can be comfortable but shifts and leaves you with a bare spot at night. Memory foam holds its shape but often sleeps hot and feels too firm for some. Latex is durable and responsive but usually comes only in fixed heights. I have tried all of these over the years, and the most practical solution I have found is a pillow that lets you add or remove fill to change the loft. That way you can adjust it after a few nights and tune it to your body.

Here are a few things I have learned to check before buying any pillow:

• Check the fill weight. A pillow that says “medium loft” can mean anything from 9 ounces to 18 ounces of fill, so look for the actual gram count.
• Look at the cover material. A breathable cotton or bamboo cover makes a real difference for temperature regulation, especially if you tend to sweat at night.
• Consider how the pillow handles compression. Press it down with your palm. If it springs back within a second or two, it has decent support. If it stays flat, it will do the same after a week of use.
• Think about washing. Pillows collect dead skin and dust mites, so a removable and machine-washable cover is not a luxury, it is a basic requirement.
• Never trust a pillow just because it feels good in the store. Your body in a store is not your body at 3 a.m. after you have been twisted into a knot for four hours.

The pillow I ended up with after all my testing turned out to be a simple filled bag with a zipper. I was skeptical at first, but the adjustable fill let me dial in the exact loft I measured. I have been sleeping on it for about six weeks now. I still wake up sometimes, but not with the neck pain that used to greet me every morning. The difference is stark enough that I walk around with a tape measure now and have checked a few friends’ pillows at their houses. Most of them are too flat or too tall, and none of them had ever measured anything.

Your pillow is not a decoration. It is the foundation of your spine alignment while you sleep, and if it is off by an inch, your body pays for it all night long. Measure it, fix it, and let your neck thank you in the morning.

If you are in the market for a new pillow, spend the extra ten minutes to measure your shoulder width and figure out your target loft. Do not just grab the first fluffy thing you see on a shelf. And if you find a pillow that lets you adjust the fill, treat that as a feature, not a gimmick. It is the only way to correct mistakes without buying a whole new pillow a month later. The right loft is not a luxury. It is a simple, measurable thing, and once you get it right, you will wonder why you ever put up with a flat lump of feathers for so long.