Graduated compression knee-high stockings

Compression Stocking Levels Explained (mmHg Guide for Canada)

By AMS Clinic Physiotherapy Team Updated June 16, 2026 5 min read ✓ Physiotherapist-reviewed

If you have ever stood in front of a wall of compression stockings wondering what "20-30 mmHg" actually means, you are not alone. Compression levels are the single most important detail to get right, and choosing the wrong one can mean a garment that feels useless, uncomfortable, or in some cases is not appropriate for you at all. This guide, curated by the physiotherapists at our Montreal clinic, breaks down the compression classes used in Canada, the conditions each level is typically associated with, and how to measure and put your stockings on correctly.

What does mmHg mean?

The number on a box of compression stockings is measured in millimetres of mercury (mmHg), the same unit used for blood pressure. It describes how much pressure the garment applies at the ankle. Medical compression is graduated: pressure is highest at the ankle and gradually decreases up the leg. This gradient is what helps support the return of blood and fluid back toward the heart, working with your muscles rather than simply squeezing the limb.

A higher number is not automatically "better." The right level depends on your symptoms, your circulation, and guidance from a qualified clinician. Browse our full range in the compression stockings & garments collection.

Compression classes explained

15-20 mmHg (mild)

This is the most common over-the-counter level and a sensible starting point for many people. It is frequently chosen for tired, aching or mildly swollen legs, for long flights or car journeys, for prolonged standing or sitting at work, and during pregnancy for general comfort. It offers noticeable support without feeling overly tight, which makes it a comfortable level for everyday wear.

20-30 mmHg (moderate / firm)

Often called "medical grade," this level is commonly associated with varicose veins, more pronounced swelling (edema), moderate venous symptoms, and recovery support. Because the pressure is firmer, many clinicians recommend confirming it is appropriate for your circulation before you start. Explore options for varicose veins if this is your primary concern.

30-40 mmHg (firm / high)

This is a stronger level typically used for more advanced venous conditions, significant edema, or as part of a clinician-directed plan. Garments at this level are generally not a self-selected purchase: they are best fitted and recommended by a healthcare professional after an assessment of your circulation.

Important: Compression at 20-30 mmHg and above can be unsuitable for people with reduced arterial circulation (such as significant peripheral artery disease). Clinicians often check circulation before recommending firmer compression. When in doubt, ask first.

Which level for which situation?

  • Travel and long flights: 15-20 mmHg is a common choice for reducing leg swelling and discomfort during prolonged immobility.
  • Varicose veins: 15-20 or 20-30 mmHg is frequently used to ease aching and heaviness. See our varicose veins collection.
  • Swelling / edema: 20-30 mmHg is commonly recommended for more noticeable swelling, ideally with clinician input.
  • Pregnancy: Many expecting parents use 15-20 mmHg for tired, heavy legs and mild swelling. Visit our maternity collection for pregnancy-friendly support.
  • Blood-clot (DVT) prevention: Compression is sometimes used as part of a broader prevention strategy, but the appropriate approach and level should be guided by your healthcare provider, especially after surgery or with personal risk factors.

These are general associations, not prescriptions. Your individual needs may differ.

How to measure and size correctly

Fit matters as much as compression level. A stocking that is too small can roll or dig in; one that is too large will not deliver effective graduated pressure. Follow these steps:

  • Measure first thing in the morning, when your legs are at their least swollen.
  • Ankle: measure the circumference at the narrowest point, just above the ankle bone.
  • Calf: measure the circumference at the widest part of the calf.
  • For thigh-length styles: also measure the upper thigh and your leg length.
  • Always compare your measurements against the specific brand's size chart rather than guessing from shoe size.

If your measurements fall between sizes or your legs differ noticeably, a clinician fitting is worthwhile.

Donning tips (how to put them on)

Compression stockings are meant to feel snug, and that can make them tricky to put on at first. These tips help:

  • Put them on in the morning, before swelling builds up over the day.
  • Make sure skin is dry. A light dusting of talc or cornstarch can help the fabric glide.
  • Don't yank in one pull. Turn the stocking partly inside out to the heel, then work it up the leg in stages, smoothing as you go.
  • Use rubber gloves for grip and to smooth out wrinkles, especially around the ankle.
  • Check the finish: seams straight, no bunching, no fabric folds that can pinch.
  • Donning aids and frames are available if reaching your feet is difficult; see our mobility aids.

When to ask a clinician

Speak with a physiotherapist, physician, or pharmacist before buying if you have diabetes, reduced arterial circulation or peripheral artery disease, numbness, skin breakdown, a known or suspected blood clot, heart failure, or any new and unexplained leg swelling (especially in one leg only). Also seek advice if you are considering 20-30 mmHg or higher, are pregnant with complications, or simply are unsure which level suits you. A short conversation can prevent discomfort and ensure the garment is genuinely helping.

Stockings are just one part of supporting your legs and mobility. If you also manage joint or back issues, you may find our back & spine support and knee braces collections useful.

Frequently asked questions

Are higher mmHg stockings always better?
No. More compression is not inherently better and can be unsuitable for some people. The goal is the lowest effective level for your needs, ideally confirmed with a clinician for 20-30 mmHg and above.

Can I wear compression stockings during pregnancy?
Many people use 15-20 mmHg during pregnancy for heaviness and mild swelling. If you have complications or significant or one-sided swelling, check with your healthcare provider first. See our maternity collection.

How long should I wear them each day?
Many people wear them through the day and remove them at night, but follow the guidance specific to your situation. They are typically put on in the morning and taken off before bed unless advised otherwise.

Do I need a prescription to buy compression stockings in Canada?
Lower levels such as 15-20 mmHg are widely available without a prescription. Firmer medical levels are best chosen with professional guidance, and some private insurance plans require a prescription for reimbursement.

Medical disclaimer

This article is provided for general educational purposes only and does not constitute medical advice, diagnosis, or treatment. Compression therapy is not appropriate for everyone, and the right compression level depends on your individual health. Always consult a qualified healthcare professional before starting compression, particularly if you have circulatory conditions, diabetes, a suspected blood clot, or new leg swelling. Never delay or disregard professional medical advice because of something you read here.

Curated and reviewed by the physiotherapists at our Montreal clinic. We select supports based on clinical experience and conservative, evidence-aware guidance — not marketing claims.