# Bike Size Calculator

URL: https://speedycalculator.com/calculators/sports/bike-size/
Last updated: 2026-10-30

> The bike size calculator recommends a frame size for road, mountain, gravel and city bikes from your height and inseam, and a wheel size for children's bikes.

## Inputs

- Bike for
- Bike type
- Rider height (cm, m, ft, in)
- Inseam (0 = estimate from height) (cm, m, ft, in)

## Results

- Inseam used
- Frame size
- Frame size
- Typical label
- Recommended wheel size

## Formula

```
Road: frame (cm) = inseam × 0.67 · Mountain: frame (in) ≈ inseam (cm) × 0.226 · City/hybrid: frame (cm) = inseam × 0.64 · Inseam ≈ 0.47 × height if unknown
```

## Explanation

Frame size is mostly about leg length (inseam) – the distance from the floor to your crotch when standing in socks. Too big and you can't straddle the bike; too small and you'll be cramped. Kids' bikes are sized by wheel diameter.

### How to use the Bike Size Calculator

- **Bike for**
- **Bike type**
- **Rider height**
- **Inseam (0 = estimate from height)**

Results update as you type, every field has its own unit menu, and everything is calculated in your browser.

### How it works

Choose adult or child bike and the type, then enter your height and, if you know it, your inseam.

### Inputs explained

FieldWhat to enterBike forChoose one: Adult, ChildBike typeChoose one: Road / gravel, Mountain bike, City / hybrid / trekkingRider heightUnits: cm, m, ft, inInseam (0 = estimate from height)Units: cm, m, ft, in

### Example values

How the main result changes when **Rider height** changes and everything else stays at the example values above:

Rider height (cm)Frame size (cm)87.528131.254117555218.7569262.583350110

## Worked example

Inputs — Bike for: Adult; Bike type: Road / gravel; Rider height: 175 cm; Inseam (0 = estimate from height): 0 cm.

Results — Inseam used = 82.3 cm; **Frame size = 55 cm**; Frame size = 21.7 in; Typical label = L.

## Key terms

- **Inseam**: Inside leg length from floor to crotch.

## FAQ

**How do I measure my inseam?**
Stand against a wall with a book between your legs and measure floor to the book's top.

**What if I'm between sizes?**
Pick the smaller frame for agility, larger for stability – and test ride.

**Why are mountain bikes sized in inches?**
Tradition; they also have shorter seat tubes for standover clearance.

**Do brands size the same?**
No – always check the brand's geometry chart.


## Sources

- [Sheldon Brown – Bicycle technical info](https://www.sheldonbrown.com/)
- [Bicycle Quarterly / Wilson – Bicycling Science (MIT Press)](https://mitpress.mit.edu/9780262538404/bicycling-science/)