Updated October 1, 2026  ·  By Mojo  ·  11 min read

Almost every dirt bike sizing guide begins with the rider’s height, and that starting point produces the wrong answer for a large number of riders. Two people of identical height can differ by several centimetres in leg length, and the seat is the part of the bike that your legs have to reach. A rider with long legs and a short torso fits a taller machine than a rider with short legs and a long torso, even though both stand at the same mark on a wall. Therefore, the measurement that decides the purchase is your inseam rather than your height. In addition, your seated reach to the controls changes with boot thickness, which is a second reason to measure in the boots you ride in. We measured seat height and kerb mass across our own range, and this guide uses those figures rather than a generic table.

One qualification before the detail, because it applies to every number below. We publish our own measurements rather than nominal catalogue values, and where we do not have a figure we say so rather than estimating one.

Why Inseam Beats Height

Your inseam decides whether you can hold the machine at a standstill, and holding the machine at a standstill is what allows you to ride the difficult parts of a trail. A rider who can place both feet near the ground recovers from a wobble without thinking, while a rider who cannot has to plan every stop in advance and avoid the ground where stops are likely. In addition, a rider who is afraid of the next stop rides more slowly and looks down more often, which slows the learning process. Consequently, the fit question is a safety question rather than a comfort question. In our experience, riders who match the machine to their inseam progress faster than riders who buy for the specification. Similarly, a rider who buys a machine they cannot hold at a standstill will spend the first season managing the bike rather than learning to ride it.

Height fails as a predictor because the ratio between leg length and overall height varies widely between individuals. A tall rider with a long torso and average legs can struggle on a machine that a shorter rider with proportionally longer legs finds comfortable. If you compare two riders of the same height, you can easily find a 40 mm difference in inseam, and 40 mm is a meaningful amount on a dirt bike seat. Therefore, a sizing chart that converts height into a seat height will be wrong for a substantial share of the people who use it. That is why we publish measurements rather than a conversion table. For example, two riders at 1.75 m can differ by 40 mm in inseam, which is the difference between a comfortable fit and a machine that is simply too tall.

There is a second reason inseam matters more on a dirt bike than on a road bike, and it concerns the ground rather than the machine. A trail rarely offers a flat, firm place to stop, so the effective ground level under your feet is often lower or less stable than a showroom floor. Consequently, a fit that feels marginal on concrete will feel inadequate on a rutted descent, where one foot lands on a high root and the other finds nothing. Similarly, a machine that fits on level ground can feel tall the first time you stop across a camber. In our experience, riders who buy a machine that fits comfortably on a showroom floor usually find it adequate on the trail, while riders who buy at the limit of their reach usually regret it.

How to Measure Your Inseam

Measuring your inseam correctly takes two minutes and one other person, and the procedure matters because small errors change the answer. Put on the riding boots you will actually wear, then stand with your back against a wall and your feet about 200 mm apart. Place a book or a rigid straight edge between your legs and raise it until it presses firmly upward, as though you were sitting on a saddle. Have your helper mark the wall at the top edge of the book, then measure from the floor to that mark. The result is your riding inseam, and it is the number that matters.

Two details change the measurement enough to matter, and both are easy to get wrong. The first is the boots, because a thick motocross sole adds height that a pair of trainers does not, and the difference can exceed 20 mm. The second is the pressure applied to the book, because a light touch reads low and a firm press reads your true seated height. Therefore, measure twice and take the larger figure rather than the average. In our experience, riders who measure in bare feet or in thin shoes end up with a number that flatters the fit and misleads the decision.

Once you have the number, keep it with you, because it turns every showroom visit into a quick decision. Ask for the seat height of the machine, compare it with your inseam, and then confirm the fit by sitting on the machine with an adult holding it upright. If the balls of both feet reach the ground comfortably, the machine is a candidate, and if they do not, the machine is wrong for you regardless of anything else. That sequence takes less time than reading a specification sheet and it produces a better answer.

The Fit Formula

The fit formula is a comparison rather than a calculation, and it has three parts. Start with your riding inseam, then add the height the machine’s seat will place you above the ground, and then check whether your feet can reach the ground with the suspension compressed slightly under your weight. If they can, the machine fits, and if they cannot, the machine is too tall for you at rest. Therefore, the question is not whether you can touch the ground with your toes but whether you can place the balls of both feet down. That distinction decides more purchases than any other single test.

Suspension compression is the part most buyers forget, and it changes the answer in your favour. When you sit on a machine, the rear suspension compresses under your weight, so the seat height you read in a specification sheet is not the height you experience while seated. A heavier rider gains more from that effect than a lighter one, which is one reason two riders of the same inseam can have different experiences on the same machine. Consequently, always measure the fit while sitting on the machine rather than beside it. In addition, wear your riding boots for the check, because the difference a sole makes is larger than most buyers assume. In our experience, that single change turns a marginal fit into an acceptable one for many riders.

Two adjustments can close a small gap if the machine is otherwise right, and both are worth knowing before you reject a model. Seat foam can sometimes be lowered, and suspension sag can be adjusted within limits, although we are not going to publish a sag figure in millimetres because we have no verified value and it depends on the rider and the model. What we will say is that a gap of a few millimetres is often solvable and a gap of 50 mm usually is not. Therefore, establish the size of the gap before deciding whether the machine is a candidate, and treat a large gap as a signal to look at a different model.

Measured Seat Heights

Our own range covers 570 mm to 960 mm in seat height and 46 kg to 122 kg in kerb mass, and that spread exists because different riders need genuinely different machines. At the small end, the KID 50 sits at 570 mm and weighs 46 kg, which suits a young beginner on flat ground. At the large end, our full-size machines reach 960 mm, which suits a tall adult on technical terrain. Therefore, the range is not a ladder of quality but a set of answers to different fit questions.

The 390 mm gap between our smallest and largest machines is larger than most buyers expect before they see the table, and it explains why a single sizing chart fails so badly. In addition, the kerb mass figure moves in the same direction, so the low machine is also the light one and the tall machine is also the heavy one. Consequently, a rider who needs a low seat also gains the benefit of a machine that is easier to lift after a fall. In our experience, that pairing makes the smaller machines better learning tools than their specification suggests.

One figure we do not publish is a conversion from inseam to seat height, and we are stating that rather than leaving a gap. We have no verified data for such a conversion, and the variation in leg length means a table of that kind would mislead as many riders as it helped. What we can do is publish the seat heights and let you compare them with your own measured inseam, which is a shorter process than it sounds. Therefore, treat any published inseam-to-seat-height chart as a rough guide rather than as a rule. In addition, the boots you wear on the day will change the answer, so measure with the equipment you actually ride in.

Fit by Rider Type

Fit resolves differently for different kinds of rider, and the differences follow from how much time each spends seated. A trail rider sits for long periods and stands for obstacles, so a machine that allows both feet down at a rest stop matters more than a few millimetres of ground clearance. A motocross rider stands for most of a moto and never stops on uneven ground, so seat height matters less than the reach to the bars and the ability to move weight forward. Consequently, the same inseam can point to different machines depending on the riding. Consider how often you stop on uneven ground, because that frequency decides whether foot placement at a standstill is critical or incidental.

A beginner fits differently from an experienced rider of the same size, and the reason is confidence rather than geometry. A new rider benefits from a machine that allows a full foot placement, because that placement removes the fear that slows learning. An experienced rider can manage a taller machine because the movements are automatic rather than deliberate. Therefore, a rider moving up a size should expect the taller machine to feel wrong for a few rides even when the fit is correct. In our experience, that feeling fades within a month if the fit is right and persists if it is wrong.

Two practical rider profiles cover most of the buyers we talk to, and both are worth describing. A shorter adult with a 760 mm inseam fits our pit bike range comfortably and will struggle on a 960 mm machine, so the low machines are the honest recommendation rather than a compromise. A taller adult with a 900 mm inseam fits a full-size machine and will find a pit bike cramped over a long ride, which makes the taller machine the better long-term choice. Our guide to where you can legally ride in Australia covers the rules that decide where those machines can be used.

When the Seat Is Too Tall

A seat is too tall when you cannot place the balls of both feet on the ground while seated, and the problem shows up in three predictable ways. The first is that you avoid stopping on slopes, which removes the most interesting terrain from your riding. The second is that you look down at the ground beside the machine rather than ahead, which slows your reactions. The third is that a slow-speed tip becomes likely rather than unlikely, because the machine leans further before you can catch it. Therefore, a tall seat is not a small inconvenience, because it changes the way you ride. Meanwhile, the rider often attributes the problem to their own skill rather than to the machine, which slows the fix.

Three options exist when a machine is too tall, and they differ in cost and in effectiveness. Buying a lower machine is the most effective option and often the cheapest, because the range covers a wide span of seat heights. Adjusting the machine is the second option, and it works when the gap is small, since seat foam and suspension adjustment can close a few millimetres. Changing your own equipment is the third, and thicker boots can help, although we are not going to quote a sole thickness because we have no verified figure for it. In our experience, buying the right machine first saves the other two steps.

One warning applies to lowering a machine rather than to buying a lower one, because the two are not equivalent. Reducing suspension travel to lower a seat changes how the machine behaves on rough ground, and it can remove the capability you paid for. Consequently, a rider who needs 50 mm less seat height should look at a smaller machine rather than modifying a large one. That conclusion is unpopular when the large machine is already in the garage, and it remains the right one.

Frequently Asked Questions

Continue Learning

• Where you can legally ride a dirt bike in AustraliaState rules and private land explained.
• Browse our dirt bike rangeYouth, pit and full-size models.
• Browse our electric dirt bikes60V and 72V platforms with swappable packs.
• Browse our ATV rangeFor riders who want four wheels.

References

Seat height and kerb mass figures in this article were measured by our own engineering team on our own machines, so they are not independent laboratory results (BSE Motor, 2026). This article was written by Mojo and reviewed by our engineering team. You can read more about us on the site, or contact our team with questions about a specific model.