Most people choose a hair extension length by guessing, then feel either short-changed or overwhelmed when the box arrives. The length on the label is measured on the hair itself, not on you, so the same 20 inches can sit in completely different places on two different people.
Here is the short answer. On a woman of average UK height, straight 16 inch extensions fall around the collarbone, 18 inch sits at the top of the bust, 20 inch reaches mid-bust, 22 inch lands just above the belly button and 24 inch sits around the waist. Your own height, where the hair is fitted on your head and your curl pattern will all move that by an inch or two. Curly and coily textures look shorter than the measurement because the curl coils up.
In this guide
- How hair extension lengths are measured
- Where each length falls on your body
- Why your height changes everything
- Why curly extensions look shorter than the label
- Does longer hair need more weight?
- Which length should you choose for a first set?
- FAQs
How are hair extension lengths measured?
Hair extension length is measured in a straight line from the top of the weft, bond or clip down to the very tip of the hair, with the hair pulled straight. That is the industry standard and it is how WAVE measures every set.
Two things follow from that. First, the measurement is taken on the hair before it goes anywhere near your head, so where it ends up depends on where your stylist places it. Hair fitted higher on the crown will finish higher than the same length fitted lower at the nape. Second, because the hair is pulled straight to be measured, any texture you add afterwards, whether that is your own curl pattern or a curling wand, will make it read shorter.
This is also why a reputable supplier will tell you the hair is double drawn. Double drawn hair has the shorter strands removed, so the set stays thick all the way to the ends rather than tapering into wisps. On longer lengths this matters more than almost anything else.
Where does each hair extension length fall?
The guide below assumes straight hair on someone around 5 foot 4 to 5 foot 6, which is roughly average height for women in the UK.
- 16 inch: collarbone, or just below it. A natural, everyday length that adds thickness without an obvious change.
- 18 inch: top of the bust. The most popular length in the UK because it reads as long without being high maintenance.
- 20 inch: mid-bust. This is where hair starts to look noticeably long.
- 22 inch: just above the belly button. A clear glamour length.
- 24 inch: around the waist. Dramatic, and it needs the weight to carry it.
16 inch sits at the collarbone on most people. It adds thickness rather than obvious length, which is why it suits anyone who wants fuller hair without announcing it.
You can shop straight by length at WAVE: 16 inch, 18 inch, 20 inch, 22 inch and 24 inch.
Why does my height change which length I need?
Because the chart above is measured on a body, not in the air. Hair length is fixed but torso length is not.
If you are 5 foot 2 or under, every length will sit roughly one to two inches lower on you than the guide suggests. A 20 inch set that hits mid-bust on someone of average height can reach the waist on a petite frame. If you are 5 foot 8 or above, the opposite happens and lengths sit higher, so 18 inch may only just clear your collarbone.
There is a quick way to check before you buy. Take a tape measure, hold the end at your ear and let it fall straight down your body. Where the number you are considering lands is roughly where your extensions will finish. It is not perfect, because extensions are fitted lower than your ear, but it is far more accurate than guessing from a photo of a model whose height you do not know.
A note for stylists
If you are fitting for a client, measure from the row placement rather than the ear. The difference between a top row and a bottom row can be two inches of finished length, and that is usually the gap between a client who is delighted and one who is not.
Best for testing a length before you commit
Straight 16 to 20 inch Deluxe Clip In 100g
Clip-ins let you try a length for an afternoon and take it out again, which is the cheapest way to find out whether 18 or 20 inch is right for you.
From £229.99 Shop now →
Why do curly hair extensions look shorter than the length on the label?
Because curls take up length. A strand of hair that measures 20 inches when pulled straight might only hang 15 inches once it springs back into its natural pattern. This is called shrinkage, and it catches people out constantly.
As a rough guide:
- Wavy (2A to 2C): looks around 1 to 2 inches shorter than the measurement.
- Curly (3A to 3C): looks around 2 to 4 inches shorter.
- Coily (4A to 4C): can look 4 to 6 inches shorter, sometimes more.
So if you want curly extensions that finish at your bust, do not order the length that reaches your bust when straight. Go up one size, sometimes two. Someone wanting a mid-bust finish in a deep wave texture is usually happiest in 22 inch rather than 20.
This set measures well past the waist pulled straight, but the curl pattern brings it back to below the shoulder blades. Always size up for texture.
The flip side is worth knowing too. Curly and coily textures carry length far better than straight hair does, because the volume fills out the ends. A 24 inch straight set can look thin at the bottom. A 24 inch deep wave set rarely does.
Best for curly and textured hair
2C/3A Deep Curly Wave Double Drawn Weft Bundles
Available from 16 to 24 inch, so you can size up for shrinkage without losing thickness through the ends.
From £229.99 Shop curly extensions →
Does longer hair need more weight?
Yes, and this is the single most common mistake we see. Length and weight are not separate decisions.
Hair naturally tapers. The longer the set, the more the ends need filling out, so a 100g pack that looks beautifully thick at 16 inch will look noticeably thinner spread over 24 inch. You have not bought a bad set. You have bought the right grams for the wrong length.
As a starting point:
- 16 to 20 inch: 100g is usually enough for a full head on medium density hair.
- 20 to 24 inch: 150g or more, otherwise the ends will look sparse.
- Fine or thin hair: you may need less weight overall, but the ratio still holds. Longer still means more.
If you are unsure, it is safer to have slightly too much hair than too little. A stylist can thin a set down. Nobody can add hair that is not there.
Best for longer lengths that need to stay thick
2C/3A Deep Wave 20 to 24 inch Deluxe Clip In 150g
The extra 50g is what keeps a 24 inch set looking full rather than stringy at the ends.
From £395.00 Shop now →
Which length should I choose for my first set?
If you have never worn extensions before, go one length shorter than the one you are picturing.
There are two reasons. Long hair is heavier and takes more looking after, and most people underestimate how much of a change even two extra inches makes. A first set that feels natural gets worn every day. A first set that feels like a costume sits in a drawer.
For most people that means 18 inch. It adds obvious length, it blends easily with shoulder-length hair and it does not demand a different routine. If your own hair is already past your shoulders, 20 inch will give you the change you are after without the jump to 22.
The other decision to get right first time is colour. Length can be trimmed. A shade that does not match cannot be fixed at home without risking the hair. WAVE offers free colour and texture matching before you buy, so it is worth using it rather than guessing from a screen.
Best for a long-term, everyday set
Nano Bond Hair Extensions
Available across every length from 16 to 24 inch, with tiny bonds that sit flat, so you can go longer without the fitting showing.
From £162.00 Shop nano bonds →
Hair extension length FAQs
How long is 18 inch hair?
18 inch hair measures a foot and a half from root to tip when pulled straight. Worn as extensions on someone of average UK height, it falls at the top of the bust, a few inches below the collarbone.
What is the most popular hair extension length in the UK?
18 inch and 20 inch account for the majority of UK sales. They give a visible change while still blending easily with shoulder-length natural hair, and they do not need the extra weight that 22 and 24 inch sets require.
Can hair extensions be cut shorter?
Yes. Human hair extensions can be trimmed and blended by a stylist exactly like your own hair, and most sets benefit from a light blend after fitting. Always have this done professionally, as cutting extensions bluntly at home can leave a hard line where they meet your own hair.
Should I measure hair extensions from my roots or my shoulders?
Neither, strictly. Extensions are measured on the hair itself, not from a point on your body. To estimate where a length will fall, hold a tape measure at your ear and let it hang straight down. That is close to where the hair will finish once fitted.
Do longer extensions damage your hair more?
Longer sets are heavier, and weight is what creates tension on the root. That said, damage comes from poor fitting and poor aftercare far more often than from length alone. A well-fitted 24 inch set on hair strong enough to carry it is safer than a badly fitted 16 inch one.
How do I know if 24 inch will be too long for me?
If you are under 5 foot 4, 24 inch will usually sit at or below your waist, which is a significant commitment in both styling time and weight. Trying a clip-in set at that length first is the simplest way to find out before investing in a permanent fitting.
Still not sure which length is right?
You do not have to work it out alone. Send us a photo of your hair and we will match your colour and texture for free before you order, and tell you honestly which length will sit where you want it. It takes a few minutes and it is the difference between a set you love and a set you tolerate.
Get your free colour and texture match →
Salon owners and stylists can also apply for a WAVE trade account for wholesale pricing across every length and texture. Browse the full range in shop all hair extensions.
