The leg should end above the point where your thigh starts widening — not on it, and not below it. That point sits in a different place on every build, which is why there is no single correct length, and why the same trunk can be perfect on one person and ride up all day on another.
Most people treat ride-up as a quality problem or a sizing problem, and go up a size to fix it. That almost never works, because the leg was not too tight — it was too long. Once you know where your own point is, the question stops being which brand and becomes which length, and that is a much easier thing to shop for.
The short answer
— The leg should end above the point where the thigh begins to widen.
— A leg ending on or below that point has somewhere to travel, so it migrates upward as you move.
— The correct length is a point on your body, not a number on a label.
— Going up a size does not fix ride-up. A shorter leg does.
— Leg opening construction helps at the margins, but length is the actual fix.
What decides the right leg length?
The shape of your thigh, not your waist size. A thigh tapers — narrow at the knee, widening as it rises toward the hip. Where a leg hem sits on that taper decides whether it stays put or climbs.
A hem that ends above the widening has nothing pulling it upward. Every time you move, the fabric is sitting on a part of the leg that is not getting bigger underneath it, so it stays where it was put.
A hem that ends on or just below the widening is in a losing position. The thigh underneath is wider than the hem circumference wants to be, so the fabric gets pushed — a little with every step, and a lot every time you sit down. By mid-morning it has gathered at the top of the thigh, which is exactly where nobody wants it.
This is why waist size is the wrong lever. Going up a size adds circumference everywhere including the leg opening, but it also lengthens the leg — so the hem lands further down the taper than before, and the problem gets slightly worse rather than better.
How do you find that point on yourself?
Sit down in a chair and look at where your thigh stops being flat and starts to spread. That is the point. A leg hem that ends above it will stay put; one that ends on it will not.
Three checks, in order of how quickly they answer the question:
- The sitting test. Sit in an ordinary chair with your feet flat. The thigh spreads under your own weight and the widening point becomes obvious. This is also the position underwear fails in, so it is the right one to test in
- The stair test. Walk up two flights in a garment you already own. If the leg has moved by the top, the hem is below your point. If it has not, it is above it
- The end-of-day test. Take note of where the hem actually sits at six in the evening rather than where you put it at seven in the morning. The gap between the two is the whole problem in one measurement
None of these need a tape measure, and that is deliberate. You are not looking for a number to shop with — brands very rarely publish leg length — you are looking for a mental picture of where the hem should land so you can judge a product photograph against it.
Why do two trunks in the same size sit differently?
Because "trunk" describes a shape, not a measurement. Leg length varies considerably between brands under the same name, and almost none of them publish the figure.
The category boundary is loose at both ends. A trunk cut long enough starts behaving like a short boxer brief; cut short enough it behaves like a brief with a token leg. Both are still sold as trunks, and both will be the same waist size as the one that fits you. Nothing on the label distinguishes them.
Rise makes it harder again. Two garments with an identical leg length will place the hem in different places if one sits higher on the hip than the other, because the whole garment has shifted up or down the body. So the number you would want — hem position relative to your thigh — is the product of two figures, neither of which is on the packet.
The practical workaround is to judge from a photograph. In a side-on product shot, look at where the hem falls relative to the crotch seam and how much thigh is covered below it. It is a rough read, but it is a better one than the size chart, which tells you nothing about leg length at all.
What each length actually feels like
Too short, right, and too long each produce a distinct daily experience. Matching what you feel to the row below tells you which direction to move in.
| Leg length | What you notice | What is happening | What to change |
|---|---|---|---|
| Too short | Bare thigh rubs on the opposite thigh; the garment feels like a brief | The hem sits so high it gives no thigh coverage at all | A slightly longer leg, or a different style |
| Right | You stop thinking about it; the hem is in the same place at night as in the morning | The hem sits above the widening and has nowhere to travel | Nothing |
| Slightly long | The hem creeps up over a few hours and needs an occasional adjustment | The hem is sitting on the widening point | A shorter leg in the same waist size |
| Too long | It gathers at the top of the thigh by mid-morning and stays there | The hem is below the widening and gets pushed up with every movement | A shorter leg — not a bigger size |
Does leg length change anything besides ride-up?
Yes — three things. It decides whether your thighs touch fabric or each other, how visible the garment is under trousers, and how much heat is held at the top of the leg.
Thigh contact is the one people feel first. A leg long enough to sit between the thighs prevents skin rubbing on skin, which matters a great deal in heat and matters not at all in winter. It is the main reason to choose a trunk over a brief, and a trunk whose leg has ridden up has stopped doing it.
Visible line is the second. A hem sitting under close-cut trousers can show, and a longer leg under lighter fabric shows more. This is about where the hem lands relative to the trouser, so it varies with what you wear more than with the garment itself.
Heat is the third and the smallest. More fabric at the top of the thigh means slightly more insulation in a part of the body that is already warm. In a hot climate it is worth a thought, though fabric choice does far more for that than leg length does.
Can you fix ride-up without changing the garment?
Not really. Leg opening construction makes a small difference, and nothing else does. If the hem is sitting below your widening point, the length is wrong and no amount of grip will hold it.
The opening can be finished in a few different ways, and a flat hem that rests against the thigh does hold better than elastic that grips it. That is a real difference and it is worth knowing about — the guide covers all three constructions and how they behave. But it operates at the margins. A well-constructed opening on a leg that is too long buys you an hour, not a day.
Washing and drying do not help either, in either direction. A garment that has relaxed slightly will return after a wash while it is still young, but that is recovery, not a change in length. Once it stops returning, the fabric has lost its recovery and ride-up will get worse rather than better.
Quick reference
— The hem should end above where your thigh starts to widen.
— Find your point by sitting down and looking, not by measuring.
— Ride-up is a length problem. Going up a size makes it slightly worse.
— Brands rarely publish leg length, so judge it from a side-on product photograph.
— Construction at the opening helps a little. Length is the actual fix.
How we build ours
Our CotCloud Trunks are cut to a genuine trunk length — short enough to sit above the widening on most builds, rather than the longer cut that has crept into the category and behaves like a short boxer brief. The leg opening is finished flat so it rests against the thigh instead of gripping it.
That will not suit everyone, because no single length can. On a longer thigh a true trunk gives less coverage than some people want, and that is a preference rather than a fault in either direction.
CotCloud is Vault & Co's name for the whole system, not just the fabric: super-combed cotton knit with Lycra at thread level, a wide flat zero-pressure waistband stitched directly to the body, flat seams, and a mid-rise no-ride-up trunk cut, developed in-house. Read what CotCloud is, or see our no ride-up trunks (build your own 3-pack).
Frequently asked questions
How long should a trunk's leg be?
It should end above the point where your thigh starts to widen. That point sits differently on every build, so the right length is a position on your body rather than a measurement. A hem above it stays put; a hem on or below it gets pushed upward as you move.
Why do my trunks ride up?
Almost always because the leg is too long for your thigh. The hem is sitting on or below the point where the thigh widens, so every step and every time you sit pushes it a little further up. Leg opening construction can slow it, but it cannot stop it.
Will a bigger size stop underwear riding up?
No, and it usually makes it slightly worse. A larger size adds circumference but also lengthens the leg, so the hem lands further down the thigh than before. The fix is a shorter leg in the same waist size.
How do I know where my thigh starts to widen?
Sit down in an ordinary chair with your feet flat and look at your thigh from the side. The point where it stops being flat and starts to spread is the one that matters, and sitting is the position where underwear fails, so it is the right position to check in.
Why do two trunks in the same size fit differently?
"Trunk" describes a shape rather than a measurement, and leg length varies widely between brands under the same name. Rise adds to it, because a garment sitting higher on the hip places the hem higher on the thigh even at the same leg length. Neither figure is usually published.
Are longer trunks better for preventing chafing?
Up to a point. A leg long enough to sit between the thighs stops skin rubbing on skin, which is the main advantage of a trunk over a brief. But a leg long enough to ride up stops doing that by mid-morning, so a shorter leg that stays put often outperforms a longer one that does not.
Does a tighter leg opening stop ride-up?
No. A gripping opening holds briefly and then slides on a moving thigh, and it tends to leave a mark while doing it. A flat hem that rests against the thigh holds better than elastic that grips it, but neither fixes a leg that is simply too long.
How can you judge leg length when buying online?
Look for a side-on product photograph and check where the hem falls relative to the crotch seam and how much thigh sits below it. Size charts do not carry leg length, so the photograph is usually the only evidence available.
What are the best trunks for thick thighs?
A true trunk length that ends above the point where the thigh widens, with a flat-finished leg opening rather than an elastic cuff. Longer legs end on the widening and get pushed up with every step. If the leg still creeps, the fix is usually a size up in the hip, not a longer leg.
What is the difference between trunks and boxer briefs?
Leg length. Trunks finish high on the thigh; boxer briefs run to mid-thigh or lower. Everything else, the pouch, the waistband and the rise, can be identical. Trunks suit shorter or wider thighs and hotter weather; boxer briefs suit long, narrow thighs where chafing between the legs is the main complaint.