Giant Bike Size Chart and Sizing Guide

Giant mountain bike sizing explained

Mountain bikes are trending towards a more flexible sizing system where you have a greater degree of personal preference. Opting for a larger frame will increase stability in a straight line while choosing a smaller frame, with a shorter top tube, will give more manoeuvrability on technical trails.

This is something we will happily discuss if you were to call our online department or pop in to any of our 6 stores in Aberdeen, Newcastle or one of the three in Edinburgh, Bruntsfield, Canonmills or Stirling.

Modern mountain bike sizing is driven by reach, which is the horizontal distance from the bottom bracket to the top of the head tube. Seat tube length matters far less than it used to, because dropper posts and long seatposts handle saddle height. Reach is what decides how roomy the bike feels when you are stood up on the pedals, and that is where you spend most of your time on rough ground.

That is why the same rider can be happy on either size in the overlap. A shorter reach turns in more quickly and feels easier to throw about on tight, technical trails. A longer reach settles down at speed and gives you more room to move around on steep descents.

Two practical points that catch people out.

Dropper post length is limited by your inside leg, not by the frame size. A rider with a shorter inside leg on a Large frame may not be able to run the longest dropper the frame will take, because the post cannot drop far enough into the seat tube to give a comfortable saddle height. If you are borderline, that is worth checking before you buy rather than after.

Wheel size can change with frame size on some Giant mountain bikes, with smaller frames built around smaller wheels so the bike still handles properly for a shorter rider. Check the model page for the size you are looking at.

For standover clearance on a mountain bike, aim for 5cm to 8cm between the top tube and your body when you stand flat-footed over the bike in socks. You need that room for the moments when you come off the pedals in a hurry.

Giant road bike size chart explained

There are three road bike models in the Giant road bikes range, the Defy, TCR and Propel. The Giant road bike size chart for these three bikes is identical, but we would warn against assuming you are the same size in all of them. Being a Medium/Large Defy does not mean that you are a Medium/Large in the TCR or the Propel. We would advise that you sit on the new model you are thinking about to make absolutely sure, especially if you are in-between sizes.

The reason the charts match but the bikes do not is stack and reach. Stack is how tall the front of the bike is. Reach is how far forward it is.

The Defy has the tallest front end and the shortest reach of the three. It puts you in a more upright position, which most riders find easier to hold for long days out and easier on the lower back.

The TCR sits lower at the front and longer in reach. It is a racier position that rewards flexibility and a bit of core strength.

The Propel is lower again, built around aerodynamics.

The practical result is that a rider who is comfortable on a Medium/Large Defy may want a Large TCR, because the lower front end on the TCR means they need a taller frame to get the bars to the same height. It works the other way too. A rider who fits a Large TCR may be better off on a Medium/Large Defy.

Here is a quick test before you choose between them. Stand with your legs straight and try to touch your toes. If you can get your palms somewhere near the floor without pain, you will probably be happy with the TCR position.

If you can only reach your shins, start with the Defy. You can always lower the front of a Defy later by taking spacers out. You cannot raise the front of a TCR much beyond what the steerer allows.

For standover clearance on a road bike, 2cm to 3cm over the top tube in socks is plenty.

Sizing for Giant bikes when you are in between sizes

It is worth discussing what happens if you are in-between sizes on the size chart, as there are either general rules or personal preferences depending on which style of bike you ride.

Road Bikes

If you are in-between sizes of a Giant road bike, the general rule is that you would size down, as you do not want to end up overstretched on a road bike. As we mentioned though, this is a general rule and some riders in the overlap will be better off going up. If you are in doubt, we are always on hand to help you with sizing.

Here is how that plays out with two real sets of numbers.

Sarah is 178cm with an 84cm inside leg and is looking at a Defy. She sits in the overlap between Medium and Medium/Large. Long legs for her height mean she needs a high saddle, and on the Medium she would end up with a lot of seatpost showing and a big drop from the saddle down to the bars. We would put her on the Medium/Large and fit a shorter stem if the reach felt long.

Tom is also 178cm, on the same bike, but with a 78cm inside leg and a longer body. Standover is not a worry for him. Reach is. The Medium with a slightly longer stem gives him a position he can hold for three hours.

Same height, same bike, different sizes. That is why we ask about inside leg before we ask about anything else.

Gravel Bikes

Similar to road bikes, if you are between sizes on a Giant gravel bike you would tend to size down. The reason for this is to have a shorter and more manoeuvrable bike, ideal for off-road, technical riding.

You would sometimes opt for a bigger size bike if you are using the bike for bikepacking, as a larger frame gives more stability when carrying more luggage, providing it is still a comfortable position for you to ride in.

Worth adding to that. A larger frame also gives you more room in the main triangle for a frame bag, which makes a difference on longer trips. If you are riding light and fast on rough ground instead, the smaller size will feel better under you.

Mountain Bikes

Mountain bike sizing has changed significantly in the last few years. Many companies have changed the geometry of their bikes to allow a choice of size based on how you would like the bike to handle.

You can opt for a smaller frame to prioritise more manoeuvrable handling for more technical trails, or a larger frame for more straight-line stability and speed for cross-country riding or flowy trails.

If you are unsure which way to go, think about where you ride most of the time. Tight woodland singletrack and slow technical climbs favour the smaller frame. Trail centre reds and blacks, bike park laps and anything fast and open favour the larger one. Size for the riding you do now, rather than the riding you are planning for next summer.

Electric Bikes

If you are between sizes on an electric version of the above bikes, road, gravel or mountain, then the same principles apply. The slightly different one is the hybrids.

If you are in-between sizes on an electric hybrid bike, you would tend to size down to make the bike more manageable in terms of size and weight, and for a more comfortable sitting position.

There is one more thing to weigh up on any e-bike. It is a good deal heavier than the same bike without a motor, which changes what manageable means. Being able to put a foot flat on the ground at a standstill counts for more when there is an extra 8kg to 10kg to hold up at a junction. 

Then add lifting it onto a car rack, wheeling it through a doorway, or getting it up a step to a flat. If the Giant bike chart size leaves you sitting right on a boundary on an e-bike, most riders are better off on the smaller one.

What can be changed after you buy

Frame size is the one decision you cannot undo. Nearly everything else can be adjusted, and knowing what can be altered takes a lot of the pressure off being between two sizes. Here is what we can change and roughly how much difference each one makes.

Stem length. Road stems typically run from 60mm to 130mm, mountain bike stems from 35mm to 80mm. Swapping a stem changes your reach by the difference between the two, so going from a 100mm to an 80mm brings the bars 20mm closer. This is the cheapest and most effective change we make.

Stem angle. Most stems can be flipped to point up or down, which moves the bars by roughly 10mm to 20mm in height depending on the angle and the length.

Spacers under the stem. Most Giant bikes arrive with 20mm to 40mm of spacers on the steerer tube. Moving the stem up raises the bars and shortens the reach a little at the same time.

Saddle position. Saddle rails give you around 20mm to 30mm of fore and aft adjustment. Changing to a seatpost with more or less setback moves it another 15mm to 25mm.

Handlebars. Road bar reach varies from around 70mm to 100mm, and drop from around 120mm to 145mm. A shorter reach bar can take 20mm out of your riding position without touching the stem. Bar width matters as well, and plenty of riders are better served by something narrower than the stock bar.

Crank length. Cranks come in 165mm, 170mm, 172.5mm and 175mm. Shorter cranks help riders with shorter legs or tight hips get a smoother pedal stroke and a more open hip angle.

What we cannot change is the wheelbase, the front centre and the standover height. Those come from the frame itself, and they are the reason the size on the chart still matters more than any of the parts above.

Giant bicycles sizing for women

Women and men tend to have different bodily proportions. Women usually have longer legs for their height while men tend to have more length in the torso.

For this reason, women often need a higher front end on the bike with a shorter reach. Giant’s sister company, Liv Bikes, manufactures bikes for this exact purpose, to be more comfortable and efficient for women. The same applies across the Liv Electric Bikes range.

That being said, not everyone fits into this general sizing rule as you do get men with longer legs and women with longer torsos. In these cases, there is still the right bike for you, but there may need to be some tweaks to the setup.

We can easily help with this as all that is usually required is a change of saddle, stem, or handlebars. We fit lots of men on Liv bikes and lots of women on Giant bikes. There are always options.

If you are on a Giant rather than a Liv and the fit is not quite there, these are the changes we make most often for female riders.

Narrower handlebars. Stock road bars are often 42cm or 44cm, and a 38cm or 40cm bar suits a lot of riders better, which improves control and takes strain out of the shoulders.

A shorter reach bar together with a shorter stem, which between them can bring the brake levers 30mm to 40mm closer without changing the frame at all.

Shorter cranks, usually 165mm, which opens up the hip angle and makes a higher cadence easier to hold.

A saddle shaped for wider sit bone spacing. We measure sit bones in store and it takes a couple of minutes.

Liv bikes are built around a different set of body proportions rather than being smaller versions of a Giant. That suits a lot of women and it suits plenty of men with longer legs as well. There is no rule here, only what fits.

Frequently Asked Questions

These are the questions we get asked most often about Giant sizing, both online and across the counter.

What size Giant bike do I need for my height?

Find your height in the chart for your type of bike above. As a rough starting point across the range, riders around 160cm to 170cm are usually a Small, 170cm to 178cm a Medium, 178cm to 186cm a Large, and above that an Extra Large.

Road bikes add an Extra Small and a Medium/Large, so the bands there are narrower. If your height falls in an overlap between two sizes, your inside leg measurement decides it, and the in-between sizes section above explains how.

What do XS, S, M, m/l, L and XL mean on a Giant bike?

They are Giant’s frame sizes, running from Extra Small through to Extra Large, with a Medium/Large on road and gravel models that sits between the two.

Giant uses letters rather than a frame measurement in centimetres because the sloping top tube on its frames means one size covers a wider range of riders than a traditional frame would.

Is a Giant Medium the same as a 54cm frame?

Roughly, but not exactly. A Giant Medium road frame fits the same riders a 54cm to 55cm traditional frame would, with a shorter seat tube and more seatpost showing.

The safest approach when you are switching brands is to work from your height and inside leg rather than from the size written on your current bike.

How do I find the frame size of a Giant bike I already own?

Look for a sticker or printed panel on the seat tube, either near the top or a little above the bottom bracket, and check the underside of the top tube as well.

If the marking has gone, the serial number stamped under the bottom bracket will let us identify the model and size for you.

How much standover clearance should I have on a Giant bike?

Stand over the top tube in socks with both feet flat on the floor. On a road bike, aim for 2cm to 3cm. On a gravel or hybrid bike, 3cm to 5cm.

On a mountain bike, 5cm to 8cm, because you need the extra room for the times you come off the pedals without planning to.

Can I ride a Giant bike that is one size too big?

You can, but it is the harder of the two choices to live with. A bike that is slightly too small can be opened up with a longer stem, a setback seatpost and a raised saddle.

A bike that is too big leaves you overstretched, and there is a limit to how short a stem you can fit before the steering starts to feel nervous. Standover clearance cannot be changed at all. If you are choosing between the two, and it is not a mountain bike where handling preference comes into it, the smaller size is the safer error to make.

Do Giant and Liv use the same size chart?

No. Liv bikes are designed around different body proportions rather than being scaled-down Giants, so they have their own geometry and their own sizing. Check the Liv chart for the model you are looking at rather than carrying your Giant size straight across.

What size Giant electric bike do I need?

Start with the electric bike chart above and your height. Then factor in the weight. A Giant electric bike is meaningfully heavier than the same bike without a motor, so being able to put a foot flat on the ground at a standstill counts for more, as does being able to lift it onto a rack or up a step. If you are between sizes on an e-bike, most riders are better off on the smaller one.

Does the Giant bike size chart change between model years?

It can. Giant updates geometry as models are redesigned, and mountain bikes have changed the most. The charts on this page cover the current range. If you are looking at a bike from an earlier year, check the geometry for that year rather than assuming the size letter means the same thing.

What happens if I need repairs or maintenance on my Giant bike?

All of our stores in Scotland and the North of England have fully-equipped workshops that can handle any Giant bicycle repair. We also have a Giant Store in Stirling. Here is the full list of our stores.

• Aberdeen
• Giant Store Stirling
• Bruntsfield, Edinburgh
• Canonmills, Edinburgh
• Giant Store Edinburgh, Stockbridge
• Newcastle

Still not sure of your size?

We hope this Giant bikes size guide has helped you settle on the right frame size for the riding you do, on road or off it, leisurely or flat out.

If you have worked through the charts and you are still not certain, send us your height and your inside leg measurement and tell us which model you are looking at. We will come back to you with a size and the reasoning behind it. 

Or pop into any of our stores, and we will measure you properly and put you on the bike so you can feel it for yourself.