Most people benefit from compression socks in the 15 to 20 mmHg range, which is enough to reduce everyday leg swelling and fatigue without a prescription. The “mmHg” number on the package tells you how much pressure the sock applies at the ankle, measured in millimeters of mercury (the same unit used for blood pressure). Compression socks range from under 15 mmHg for light everyday use up to 40 mmHg or higher for serious medical conditions.
Choosing the right level depends on what you’re using them for. Here’s how each range works and who it’s best suited for.
What the Compression Ranges Mean
Compression socks are sold in defined pressure ranges. The number always refers to the pressure at the ankle, which is where it’s highest. From there, the pressure gradually decreases as it moves up your leg toward the knee or thigh. This gradient design pushes blood upward, helping your veins return blood to the heart more efficiently.
- Light (under 15 mmHg): Minimal pressure for general comfort. Not considered medically therapeutic.
- Mild (15 to 20 mmHg): The most common over-the-counter level. Reduces occupational swelling and leg tiredness.
- Medium/Firm (20 to 30 mmHg): Treats moderate swelling, varicose veins, and helps prevent blood clots. Often requires a prescription.
- High (30 to 40 mmHg): Used for chronic venous insufficiency, lymphedema, and venous ulcer healing. Always prescribed by a provider.
Socks below 20 mmHg are widely available without a prescription and are what most healthy people reach for. Once you get into the 20 to 30 mmHg range and above, a healthcare provider should be involved to make sure the pressure is appropriate and safe for your circulation.
Under 20 mmHg: Everyday and Occupational Use
If you stand or sit for long stretches at work, travel frequently, or just notice your legs feeling heavy by the end of the day, socks under 20 mmHg are a good starting point. Research shows that 15 to 20 mmHg stockings significantly reduce leg swelling over the course of a workday compared to wearing no compression at all, regardless of whether you mostly sit, mostly stand, or alternate between the two. In one study, the reduction in swelling was consistent across all three work positions.
This range is also popular among pregnant women dealing with mild ankle swelling and among travelers on long flights who want to reduce the risk of leg discomfort. You don’t need a fitting or a prescription. Most pharmacies and online retailers carry them, and they’re comfortable enough to wear all day.
20 to 30 mmHg: Moderate Medical Conditions
This is the most commonly prescribed medical-grade level. Vascular specialists typically recommend 20 to 30 mmHg compression for people dealing with noticeable varicose veins, significant leg swelling, or a history of deep vein thrombosis (DVT). The added pressure helps veins that aren’t functioning well on their own, reducing the pooling of blood in the lower legs.
For varicose veins specifically, this level can reduce both the visible bulging and the aching, heavy feeling that comes with it. After a DVT, medium-pressure stockings help manage the residual swelling and pain that can linger as part of post-thrombotic syndrome. Providers generally start here when there’s significant swelling but reserve higher levels for more severe cases.
30 to 40 mmHg: Severe Swelling and Ulcers
High-compression stockings at 30 to 40 mmHg are reserved for chronic conditions that cause substantial fluid buildup or skin breakdown. The strongest evidence at this level is for venous ulcer healing. A Cochrane review of four trials found that high-compression stockings were more effective than moderate-compression stockings at promoting ulcer healing and preventing recurrence.
This range is also used for moderate to severe lymphedema, where protein-rich fluid accumulates in the legs because the lymphatic system can’t drain properly. In general, the highest compression a person can tolerate tends to produce the best results for lymphedema, though lower levels work for milder cases. People with chronic venous insufficiency that has progressed to skin changes or ulceration are also candidates for this level. These stockings are noticeably tighter and harder to put on, so your provider may recommend a donning device to help.
Compression for Exercise and Recovery
Athletic compression socks typically fall in the 15 to 20 mmHg range, with graduated pressure from ankle to calf. Research on recovery-focused compression found that wearing socks during the hours after exercise increased blood flow velocity in the deep veins of the leg compared to both a placebo sock and no compression at all. This faster blood flow helps clear the metabolic byproducts of exercise from muscle tissue, reduces post-workout swelling by limiting the space available for fluid to accumulate, and may speed nutrient delivery to recovering muscles.
The performance benefits of wearing compression during exercise are less clear-cut, but the recovery benefits are more consistently supported. If you’re choosing compression socks for running, lifting, or other sports, 15 to 20 mmHg is the standard athletic level.
How Graduated Compression Works
All quality compression socks use a graduated design, meaning the pressure is strongest at the ankle and decreases as it moves up the leg. A sock rated at 20 mmHg, for example, delivers about 20 mmHg at the ankle but only around 15 mmHg at mid-calf. This pressure gradient mimics and supports the calf muscle pump, the natural mechanism your body uses to push blood back toward the heart against gravity.
When the veins in your lower legs are compressed, their diameter narrows, which increases the speed of blood flowing through them. Faster venous return means less blood pools in the legs, less fluid leaks into surrounding tissue, and less swelling develops over the course of the day. The same mechanism helps reduce the risk of blood clots during periods of immobility, because stagnant blood flow is one of the key triggers for clot formation.
Getting the Right Fit
Compression level matters, but so does size. A sock that’s too large won’t deliver its rated pressure, and one that’s too small can create uncomfortable pressure points or even restrict circulation. For knee-length 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-length stockings, add your upper thigh circumference at the buttock fold and the full leg length from heel to buttock.
Take measurements in the morning before any swelling develops, since your legs are at their smallest then. Each manufacturer has its own sizing chart, so check the specific brand’s guide rather than assuming a size carries over. If you’re between sizes, sizing up usually provides a more comfortable fit while still delivering therapeutic pressure.
Who Should Avoid Compression
Compression socks are not safe for everyone. People with peripheral artery disease (PAD), where blood flow to the legs is already restricted, can experience serious complications from external compression. The critical threshold is an ankle-brachial index (a simple test comparing blood pressure in your ankle to your arm) below 0.6, or an ankle pressure below 60 mmHg. Below those numbers, sustained compression is contraindicated because it can further compromise already limited blood supply to the foot and lower leg.
Even with milder arterial disease (an index between 0.6 and 0.9), compression should be used cautiously and monitored for signs that it’s impairing circulation, such as increased pain, color changes in the toes, or numbness. If you have diabetes, neuropathy, or any condition that affects blood flow to your legs, get clearance before using compression socks at any level.