Compression 101
Medical compression socks: how 20-30 mmHg actually works
If a clinician has recommended compression, or you're weighing it for flying, pregnancy, varicose veins, lymphedema, or post-surgical recovery, start here. This clinician-reviewed guide covers what mmHg means, how to size correctly, how to wear the socks day to day, and how to keep them working.
In this guide
What does 20-30 mmHg mean?
mmHg stands for millimeters of mercury, the same unit your blood pressure is measured in. "20-30 mmHg" means the sock applies between 20 and 30 millimeters of mercury of pressure to your leg, with the firmest compression at the ankle and gradually less compression as the sock moves up toward the knee.
It's the prescription-strength level vascular clinicians most commonly recommend, well above the 15-20 mmHg "lifestyle compression" most consumer brands sell, and a step below the 30-40 mmHg level reserved for advanced lymphedema and severe venous disease. It's the level the American College of Chest Physicians recommends for travelers with VTE risk factors on flights longer than 6 hours.
How graduated compression actually works
When you're standing or sitting still, gravity pulls blood and lymphatic fluid downward into your lower legs. Healthy leg veins have one-way valves that, combined with your calf muscle contractions, push the blood back up to your heart. When those valves are weak or damaged, blood pools, leading to swelling, aching, varicose veins, and in serious cases venous ulcers or deep vein thrombosis (DVT).
Graduated compression replicates what a healthy calf muscle pump does. A Cochrane meta-analysis of 12+ randomized trials in roughly 2,856 air travelers found graduated compression stockings reduced asymptomatic DVT by approximately 90% compared to no stockings.
Compression sock levels explained
| Level | What it's for | Typical user |
|---|---|---|
| 8-15 mmHg | Mild support, all-day comfort | Office workers, mild leg fatigue |
| 15-20 mmHg | Mild medical, travel, mild varicose | Frequent travelers, mild pregnancy swelling |
| 20-30 mmHg | Prescription-strength moderate compression | CVI, varicose veins, post-surgical, nurses, DVT prevention |
| 30-40 mmHg | Strong medical compression | Severe venous disease, lymphedema |
| 40-50 mmHg | Maximum compression | Severe lymphedema, clinician-supervised |
How to size compression socks correctly
Sock size in compression is not based on shoe size. The two measurements that matter are:
- Ankle circumference, smallest part, just above the bony bump.
- Calf circumference, widest part.
Measure first thing in the morning, before you've been standing, that's when your leg is at its smallest. If your calf is at or near the upper limit of a size range, choose the wide-calf option. See Ovena's compression sizing chart →
How to put compression socks on (with a sock aid)
- First thing in the morning, before standing up.
- Turn the sock inside out down to the heel. Place your foot in the heel pocket.
- Roll the sock up your leg, smoothing wrinkles as you go.
- Check the heel position and make sure the top isn't folded over.
If you have arthritis, limited mobility, or recent surgery, a sock aid donning device removes the difficulty.
Common uses
Long flights and travel
ACCP recommends graduated stockings for travelers with VTE risk factors on flights longer than 6 hours.
Nurses and 12-hour shifts
20-30 mmHg is the standard for anyone on their feet all day.
Pregnancy
Commonly used in the second and third trimesters for swelling and varicose vein discomfort. Confirm with your OB-GYN before starting.
Tired, achy legs at end of day
Often dramatic improvement within the first week.
How to wash compression socks so they last
Most compression socks lose elasticity in the wash, not from the wear. Standard laundry detergent is alkaline (pH 9-10), which catalyzes hydrolysis of the polyurethane bonds in spandex and elastane.
- Use a pH-balanced compression cleanser (pH 5-7). Ovena's cleanser →
- Hand wash or delicate cycle in cool water.
- Don't use fabric softener, coats the fibers.
- Don't put them in the dryer on heat. Air dry flat.
- Wash after every wear if you can.