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Stack and reach calculator

Two frames rarely differ by one number. Enter the bike you ride with its cockpit, then the frame you are comparing, and see which stem and spacers would put your hands back where they are now.

The bike you ride
The frame you're comparing

Stack is +20 mm and reach -8 mm against your bike. Both numbers come straight from the manufacturer’s geometry chart.

To sit the same on the other frame

100 mm -6° stem, 0 mm spacers

That lands within 3 mm of where your hands are now, with parts any shop stocks. Spacers can be added but never taken below the head tube, so a frame with less stack is easier to fix than one with more.

Open Bike Fit

Paste a whole geometry chart and compare every size at once.

What stack and reach actually are

Both are measured from the centre of the bottom bracket to the top of the head tube: stack is the vertical distance, reach the horizontal one. They describe the frame without any parts attached, which is why they compare across brands when a size label cannot. They do not tell you where your hands go — the headset cap, spacers, stem and handlebar all sit on top of that point.

Stack is the harder one to fix

Reach is adjustable in both directions with stem length. Stack is not: you can add spacers to raise the bar, but you cannot go below the head tube, and most forks cap the spacer stack around 30–40 mm. A frame with slightly less stack than you need is a cheap fix; one with too much is not.

The two move together

Adding spacers pulls the bar back as well as up, because the steerer leans back; a longer stem pushes the bar forward and slightly up. So a taller, shorter frame can often be matched with a longer, lower stem — and the calculator searches for that combination rather than making you guess.

When the answer is "no"

If nothing ordinary reaches your position, the frame is the wrong size for you rather than a stem away from it. Stock stems run 70–120 mm; needing 140 mm or 50 mm to make a bike work is the clearest signal a geometry chart can give you before you buy.

Check a whole bike, not one numberBike Fit takes your measurements and a geometry chart and gives the full starting setup — plus what to adjust.

Comparing bikes by stack and reach

Stack and reach are the two numbers that let you compare frames across brands, because they ignore size labels and tube lengths entirely. What they do not do on their own is tell you whether a bike will fit: the cockpit sits between the frame and your hands, and it moves them in two directions at once.

This calculator closes that gap. It takes your current frame and cockpit, works out where your hands sit, then searches the other frame for the stem and spacer combination that reproduces the same position — the same solver the Bike Fit tool uses.

Frequently asked questions

What is stack and reach on a bike?+

Stack is the vertical distance from the centre of the bottom bracket to the top of the head tube; reach is the horizontal distance between the same two points. Together they describe the frame independently of size labels and tube shapes, which is what makes cross-brand comparison possible.

How do I compare two bikes with different stack and reach?+

Work out where your hands sit on the bike you ride, then find the stem length, stem angle and spacer height that put them in the same place on the other frame. That is what this calculator does; comparing the raw stack and reach numbers alone is misleading because the cockpit changes both.

Is more stack better?+

Neither is better — more stack means a more upright front end. What matters is direction: stack can be raised with spacers but not lowered below the head tube, so a frame with a little less stack than you want is easier to adapt than one with too much.

How much stack does 10 mm of spacers add?+

About 10 mm of height, and it also pulls the bar roughly 3 mm closer, because the steerer leans back as it rises. Most forks allow 30–40 mm of spacers in total.

Can a stem fix any difference in reach?+

Within limits. Stock stems run 70–120 mm, so about 50 mm of adjustment either way, and each 10 mm also moves the hands about 2 mm vertically. If matching your position needs a stem outside that range, the size is at the edge for you.

Related reading

Bike Fit: check a whole bikeStem length calculatorSaddle height calculator