The type of compression socks you need depends on two things: how much pressure your legs require and how high the sock needs to reach. Most people looking for everyday relief from tired, achy legs or mild swelling do well with 15 to 20 mmHg knee-high socks. But if you’re dealing with varicose veins, recovering from surgery, or managing a chronic condition, you likely need something firmer or longer. Here’s how to figure out exactly what fits your situation.
Compression Levels by Pressure
Compression socks are rated in millimeters of mercury (mmHg), which measures how much squeeze they apply to your legs. The pressure is always highest at the ankle and gradually decreases as the sock moves up your leg, pushing blood back toward your heart. Higher numbers mean a tighter sock.
8 to 15 mmHg (light support): These feel like a snug regular sock. They’re useful for mild leg fatigue after a day of standing or sitting, and for occasional travel. You can buy them without any medical guidance.
15 to 20 mmHg (mild support): This is the most popular range for self-selected compression. It handles mild swelling, early-stage varicose veins, and general leg heaviness. It’s also the level often recommended for pregnant women with mild edema and for people building up tolerance to compression for the first time. If you’ve never worn compression socks before, this is a sensible starting point.
20 to 30 mmHg (moderate, often called Class I): The most common therapeutic range. This level provides meaningful support for visible varicose veins, moderate swelling, and post-surgical recovery. Pregnant women with more pronounced swelling or varicose veins often benefit from this range over the milder option. It’s also widely used for daily maintenance after lymphedema treatment.
30 to 40 mmHg (firm, often called Class II): Reserved for severe venous insufficiency, lower-extremity lymphedema, and conditions where lighter socks haven’t controlled swelling. At this level, you should be working with a healthcare provider to confirm the socks are appropriate, because applying this much pressure to legs with poor arterial circulation can be dangerous.
40 to 50 mmHg and above (very firm, Class III+): Only used for severe lymphedema or cases that clearly fail at lower levels, and only after clinical assessment.
One Important Caveat About Pressure Ratings
There are no standardized regulations governing how manufacturers rate compression socks. The actual pressure a sock delivers varies based on your leg size, so a sock labeled 20 to 30 mmHg may feel quite different on a narrow calf than on a wider one. Dr. Eri Fukaya, a vascular specialist quoted by the American Heart Association, suggests thinking of compression in terms of how it feels rather than fixating on exact numbers: start with a medium level and adjust to milder or firmer based on comfort.
Knee-High vs. Thigh-High vs. Waist-High
Knee-high socks are the default choice for most people. They cover the area where blood pools most readily (the lower leg and ankle), they’re easier to put on, and people are far more likely to wear them correctly and consistently. Patient adherence is notably higher with knee-length socks compared to thigh-length, and an incorrectly worn compression garment can actually be unsafe, bunching up and creating a tourniquet effect.
Thigh-high stockings may offer a slight edge for preventing deep vein thrombosis in surgical patients. A systematic review from the University of York found a trend favoring thigh-length stockings for DVT prevention, with a 73% probability of being the most effective option, but the difference was not statistically significant. The practical tradeoff is that thigh-highs slip, roll, and frustrate people enough that many stop wearing them or wear them improperly.
A reasonable approach: choose thigh-high or waist-high garments only if your swelling or condition extends above the knee, or if your provider specifically recommends it. Otherwise, knee-highs are the better everyday choice because you’ll actually wear them.
Choosing by Your Specific Situation
Travel and Long Flights
If you’re a generally healthy person taking a short flight, you probably don’t need compression socks at all. The American Society of Hematology guidelines don’t recommend them for low-risk travelers on short flights. For longer flights, the guidelines suggest compression only for people at higher risk of blood clots, such as those with a history of DVT, recent surgery, or clotting disorders. If you do want a pair for comfort on a long-haul flight, 15 to 20 mmHg knee-highs are standard.
Pregnancy
Swollen feet and legs are common during pregnancy as blood volume increases and the growing uterus puts pressure on veins. Light, breathable compression socks help improve blood flow and reduce painful swelling. Start with 15 to 20 mmHg for mild puffiness. If you develop visible varicose veins or more significant swelling, 20 to 30 mmHg socks offer stronger support. Look for socks in moisture-wicking fabric, since pregnancy already raises your body temperature.
Varicose Veins
For early or mild varicose veins, 15 to 20 mmHg provides enough counter-pressure to ease symptoms. Once veins are clearly visible and accompanied by moderate swelling, aching, or skin changes, 20 to 30 mmHg is the standard therapeutic range. Severe venous insufficiency with significant skin damage or ulceration typically calls for 30 to 40 mmHg under medical supervision.
Exercise and Recovery
Compression socks are popular among runners and athletes who believe they reduce soreness and speed recovery. The marketing is persuasive, but as Harvard Health Publishing notes, there isn’t convincing scientific evidence that compression socks improve athletic performance or meaningfully shorten recovery time. If they feel good to you during or after a run, there’s no harm in wearing them. Just don’t expect them to replace proper rest and recovery strategies. Most athletic compression socks fall in the 15 to 20 mmHg range.
Material and Fabric
The fabric matters more than most people realize, especially if you plan to wear compression socks for hours at a time.
Synthetic moisture-wicking fibers (often marketed under names like Coolmax) are the best performers for keeping feet dry. Their structure pulls sweat away from skin and allows it to evaporate faster than natural fibers. They also hold up well over time, with strong durability and dimensional stability, meaning the sock keeps its shape and compression through many washes.
Cotton feels the softest against skin and is the most comfortable in terms of texture. But cotton absorbs moisture quickly and releases it slowly, which means your feet stay damp. That makes cotton a poor choice for all-day wear, hot climates, or exercise.
Acrylic blends land in the middle. They wick moisture better than cotton, won’t stick to wet skin, and provide the highest thermal insulation, making them a solid pick for cold-weather use.
Nearly all compression socks use nylon and spandex (Lycra) as their structural base to deliver the actual compression. The fiber listed on the label, whether cotton, synthetic, or wool, typically refers to the outer or inner layer that touches your skin. Heavier, thicker fabrics take longer to dry, so if moisture is a concern, choose a lighter-weight option.
How to Get the Right Size
A compression sock that’s too loose won’t deliver enough pressure. One that’s too tight can restrict circulation. Sizing is based on circumference measurements, not shoe size.
For knee-high socks, you need two measurements: your calf circumference at its widest point, and the length from the back of your heel to the bend of your knee. For thigh-high stockings, add two more: the circumference of your upper thigh at the crease where your leg meets your buttock, and the full length from your heel to that same fold.
Take these measurements first thing in the morning before any swelling develops, or at whatever time of day your provider recommends. Use a flexible tape measure, keep it snug but not pulled tight, and compare your numbers to the manufacturer’s sizing chart. Every brand sizes differently, so don’t assume a medium in one brand matches a medium in another.
When Compression Socks Are Unsafe
Compression socks are not safe for everyone. The main concern is peripheral artery disease, a condition where narrowed arteries already limit blood flow to the legs. Adding external compression on top of that can further restrict circulation, potentially worsening the blockage and causing tissue damage. If you have known arterial disease, reduced pulses in your feet, or pain in your calves when walking that resolves with rest, get clearance from a provider before wearing any compression garment. People with severe neuropathy who can’t feel whether socks are too tight should also exercise caution, since they may not notice early signs of problems like skin breakdown or restricted blood flow.