Advanced Reach and Stack Calculator
Formula Used
Survey stack = Head tube top height from floor − Bottom bracket height from floor.
Survey reach = Horizontal distance from bottom bracket plumb line to head tube top.
Steerer lift = Spacer stack height + Headset cover height.
Steerer reach change = −Steerer lift × cos(head tube angle).
Steerer stack change = Steerer lift × sin(head tube angle).
Stem reach change = Stem length × cos(stem angle).
Stem stack change = Stem length × sin(stem angle).
Cockpit reach = Frame reach + Steerer reach change + Stem reach change + Handlebar extra reach.
Cockpit stack = Frame stack + Steerer stack change + Stem stack change + Handlebar extra stack.
How to Use This Calculator
- Select your input unit.
- Choose known frame values or survey measurements.
- Enter frame reach and stack, or enter measured floor values.
- Add head tube angle, spacers, headset cover, stem length, and stem angle.
- Add handlebar reach or drop if you want cockpit values.
- Enter target cockpit values when comparing another setup.
- Press the calculate button.
- Download the result as CSV or PDF.
Example Data Table
| Bike Type | Frame Reach | Frame Stack | Stem | Spacers | Typical Note |
|---|---|---|---|---|---|
| Road endurance | 375 mm | 585 mm | 90 mm | 25 mm | Taller and calmer position. |
| Road race | 395 mm | 550 mm | 110 mm | 10 mm | Lower and longer position. |
| Gravel | 390 mm | 570 mm | 80 mm | 30 mm | Stable mixed-surface setup. |
| Flat bar commuter | 410 mm | 610 mm | 70 mm | 35 mm | Upright daily riding setup. |
Reach and Stack Basics
Reach and stack describe a rider’s front triangle. Reach is the horizontal distance from the bottom bracket to the top of the head tube. Stack is the vertical distance between those same points. These two numbers explain frame height and length better than seat tube labels.
Why This Calculator Helps
Small changes can feel large on a bicycle. A taller spacer stack raises the bars and usually shortens effective reach. A longer stem moves the hand position forward. Stem angle changes both height and distance. This calculator combines those effects in one place. It also lets you compare a measured setup against a target setup.
Using Direct Measurements
Use direct mode when you already know frame reach and frame stack. Most frame charts list both values. Enter them in millimeters or inches. Add head tube angle, spacers, headset cover height, stem length, stem angle, and handlebar offsets. The result shows frame values and cockpit values.
Using Survey Measurements
Use survey mode when you measure a real bike. Place the bike on level ground. Drop a plumb line from the bottom bracket. Measure forward to the head tube top center. Then measure both vertical heights from the floor. Stack equals head top height minus bottom bracket height.
Reading The Result
The cockpit reach is the final horizontal hand reference. The cockpit stack is the final vertical hand reference. Positive target difference means the calculated setup is larger. Negative difference means it is smaller. Use these numbers before buying a stem, cutting a steerer, or changing bars.
Fit Notes
The calculator is a planning guide. It does not replace a professional bike fit. Body proportions, flexibility, shoe position, saddle setback, and riding style all matter. Still, reach and stack give a clear starting point. They help riders compare bikes, document changes, and avoid guesswork during setup.
Export And Record Keeping
Save each result with the buttons. The table gives common examples for checking your entries. Keep notes for every change. Record the stem, spacers, bars, and date. This makes repeat testing easier. It also helps when comparing two bikes with similar chart numbers. Accurate records turn fit changes into simple decisions, not repeated workshop guesses during future adjustments.
FAQs
1. What is bike reach?
Reach is the horizontal distance from the bottom bracket center to the top center of the head tube. It helps show how long the frame feels before adding stem and handlebar effects.
2. What is bike stack?
Stack is the vertical distance from the bottom bracket center to the top center of the head tube. A larger stack usually supports a taller handlebar position.
3. Should I use known mode or survey mode?
Use known mode when you have geometry chart values. Use survey mode when measuring a real bike with a floor, plumb line, tape measure, and level reference.
4. Why does spacer height reduce reach?
Spacers follow the angled steerer tube. Because the steerer leans backward, adding height also moves the stem clamp slightly rearward, reducing effective cockpit reach.
5. What does negative stem angle mean?
A negative stem angle means the stem points downward from horizontal. It usually lowers cockpit stack while keeping most of the stem’s forward reach.
6. Can I compare two bikes?
Yes. Calculate the first bike, save the values, then enter target reach and stack from another bike. The difference fields show how far apart they are.
7. Does this replace a bike fit?
No. It supports planning and comparison. Comfort also depends on saddle position, flexibility, crank length, shoes, riding goals, and personal movement patterns.
8. Can I use inches?
Yes. Select inches before entering values. The calculator converts internally and still exports clear results with both selected-unit and millimeter values.