mmHg is millimeters of mercury - a pressure unit. On a compression sock it describes the pressure at the ankle, where the sock is tightest. A “20-30 mmHg” sock applies 20 to 30 mmHg at the ankle and progressively less up the leg. That gradient is the entire mechanism, and a sock without it is just a tight sock.
The levels, and what each is for
Compression levels and their typical indications| Level | Name | Typically for |
|---|
| 8-15 mmHg | Light | Mild tired legs; closer to a supportive sock than a compression one |
| 15-20 mmHg | Moderate | General prevention - leg fatigue and heaviness from standing. Where most people should start |
| 20-30 mmHg | Firm | Established varicose veins, chronic ankle swelling, previous clot - per published podiatric guidance |
| 30-40 mmHg and above | Medical | Prescribed and clinically supervised. Not a self-selected level |
Which level should you buy?
If nothing is visibly wrong and your legs just ache: 15-20 mmHg. This is the honest default and it is where published guidance points for general nursing use.
If you have established swelling, visible varicose veins or a previous clot: 20-30 mmHg is where published podiatric guidance points. That same guidance adds a caveat worth repeating: while 20-30 is available over the counter, having a clinician confirm the right indication and sizing is recommended.
If a clinician has told you a level: that level. Buying down because the firmer ones are a struggle to put on defeats the purpose entirely.
The practical difference nobody mentions
20-30 mmHg is substantially harder to get on than 15-20. Not slightly - noticeably. At 6am before a shift, on a tired body, that is the difference between wearing them and leaving them in a drawer.
This is the single most common reason people decide compression socks are not for them. They buy the firmer level because more sounds better, find the morning fight unbearable, and quit the category entirely. Starting at 15-20 and working up avoids that, and a sock you actually wear at 15-20 beats one you do not wear at 20-30.
If you need the firm level and struggle: put them on before you get out of bed, when your legs are at their least swollen; turn the sock inside out to the heel and roll it up rather than pulling; and consider a donning aid, which exists precisely for this.
More is not better
Worth being explicit, because the instinct is strong. Compression is not like cushioning where more is generally better. Too much pressure for your situation can be uncomfortable, can leave marks, and in some circumstances is actively inadvisable.
In particular: if you have peripheral arterial disease, diabetes with neuropathy, or any condition affecting arterial circulation or sensation, compression is a clinical decision and not one to make from a product page. The level that helps a venous problem can be the wrong choice for an arterial one.
Calf size matters as much as level
A correctly-sized 15-20 mmHg sock does its job. An undersized 20-30 mmHg sock constricts at the calf with no gradient below it, which is worse than either. Measure the widest part of your calf in the evening and use the brand’s published chart - over 17 inches, go wide.
What we cannot tell you
Nobody at Shift & Sole holds a clinical credential. We can tell you what the levels mean, what published guidance says about indications, and what the practical trade-offs are. We cannot tell you which level is right for your legs - and if you have any diagnosed circulation condition, that question belongs with the person treating you rather than with a gear site.
