The numbers 15-20 mmHg and 20-30 mmHg refer to compression levels in compression socks and stockings, measured in millimeters of mercury. The difference comes down to how much pressure the garment squeezes against your legs: 15-20 mmHg is mild compression for everyday prevention and minor symptoms, while 20-30 mmHg is firm, medical-grade compression for diagnosed conditions and more significant swelling. Choosing between them depends on what’s happening with your legs and why you need compression in the first place.
What the Numbers Actually Mean
MmHg stands for millimeters of mercury, the same unit used to measure blood pressure. In compression garments, the number tells you how tightly the fabric presses against your skin. A 15-20 mmHg sock applies 15 mmHg of pressure at its lightest point (usually near the knee) and 20 mmHg at its strongest point (typically around the ankle). This graduated design pushes blood upward, helping it return to your heart instead of pooling in your lower legs.
A 20-30 mmHg garment works the same way but with noticeably more squeeze. That extra pressure makes a real difference for people dealing with vein problems, chronic swelling, or blood clot risk. The jump from 20 mmHg at the top end of the mild range to 30 mmHg at the top of the firm range represents a 50% increase in maximum pressure, which is why these two levels are suited to very different situations.
When 15-20 mmHg Is the Right Choice
The 15-20 mmHg range is what most people encounter first. It’s often labeled “mild” compression and covers everyday scenarios where your legs feel tired, achy, or mildly swollen but you don’t have a diagnosed vein condition. Common reasons to wear this level include:
- Long periods of sitting or standing, such as office work, driving, or flights
- Very early or mild swelling that comes and goes throughout the day
- Prevention during travel, especially air travel after lymph node procedures or surgery
- Building tolerance if you’re new to compression and need to get used to the sensation before moving to a higher level
- Sports and general leg fatigue, where the goal is comfort rather than treating a medical condition
You can buy 15-20 mmHg compression socks over the counter at drugstores, medical supply stores, and online without a prescription. They’re widely available in athletic styles, dress socks, and knee-highs. For most healthy people who just want some extra leg support, this level is sufficient.
When 20-30 mmHg Is Necessary
The 20-30 mmHg level is the most commonly prescribed compression strength. It’s classified as firm, medical-grade compression and is typically recommended for people with a specific diagnosis or significant symptoms. Conditions that call for this level include:
- Varicose veins that are visible and symptomatic
- Chronic venous insufficiency, where leg veins don’t efficiently return blood to the heart
- Moderate to severe edema (persistent leg swelling)
- DVT prevention or history of blood clots
- Post-surgical recovery, particularly after vein procedures or orthopedic surgery
- Lymphedema with significant swelling
- POTS or orthostatic hypotension, where blood pressure drops when standing
Healthcare workers like nurses who spend 12-hour shifts on their feet often wear 20-30 mmHg socks as well. Athletes sometimes use this level during recovery from intense training, though the mild range is more common for general athletic use.
While no law requires a prescription for 20-30 mmHg garments, most pharmacies and medical supply stores won’t dispense them without one. Sigvaris, a major compression garment manufacturer, notes that certain individuals may be at risk of harm from higher compression levels due to contraindications, so doctor oversight is recommended at this strength and above.
How They Feel to Wear
At 15-20 mmHg, you’ll feel a gentle, steady hug around your legs. Most people find this comfortable enough to wear all day without adjustment. Putting them on is straightforward, and they don’t feel dramatically different from a snug athletic sock.
At 20-30 mmHg, the pressure is unmistakable. The socks are harder to pull on (many people use donning gloves or a stocking donning aid), and the squeeze is firm enough that you’ll feel it throughout the day. For people with significant swelling or vein problems, this pressure often brings relief. But if your legs don’t actually need that level of compression, 20-30 mmHg can feel uncomfortably tight and may even cause issues like skin irritation, redness, or bruising.
If you’ve never worn compression before, starting at 15-20 mmHg to build tolerance is a common approach. Jumping straight to 20-30 mmHg can be discouraging if the tightness feels overwhelming, even if that’s ultimately the level you need.
Why Correct Sizing Matters More Than the Number
The pressure printed on the package only holds true if the garment fits your leg correctly. Research on compression garments shows that the actual pressure delivered is significantly affected by garment size and the wearer’s body dimensions. An oversized garment delivers substantially less pressure than the label claims, while an undersized garment delivers more, potentially too much.
This means a poorly fitting 20-30 mmHg sock could deliver less compression than a well-fitting 15-20 mmHg one. Most compression brands provide measurement guides that ask for your ankle circumference, calf circumference, and sometimes leg length. Taking these measurements accurately, ideally first thing in the morning before any swelling sets in, is essential to getting the right pressure.
If the top band of a knee-high or thigh-high stocking is too tight, it can create a tourniquet effect that actually blocks blood flow instead of improving it. Signs of a poor fit include numbness, tingling, increased pain, skin indentations that last a long time after removal, or discoloration in your toes.
Who Should Avoid Higher Compression
Compression stockings are not safe for everyone. People with severe peripheral artery disease (PAD) should not wear compression socks at either level because PAD already narrows the blood vessels in the legs, and external pressure can further reduce blood flow. This is one of the main reasons higher compression levels are typically sold with medical guidance.
Other situations where compression can cause harm include active skin infections on the legs, open wounds, or conditions that affect skin integrity. If you have diabetes with peripheral neuropathy, you may not feel warning signs like pain or numbness that indicate the compression is too tight, making careful sizing and medical input especially important.
For most people choosing between these two levels, the decision is straightforward: if your legs feel tired and you want preventive support, 15-20 mmHg handles that well. If you have a diagnosed vein condition, chronic swelling, or a history of blood clots, 20-30 mmHg provides the therapeutic pressure those conditions require.