Giro
Register II MIPS
Everyday adult helmet with MIPS and a simple dial fit.
Universal Adult, 54–61 cm
View on AmazonPrice and availability on Amazon
Free tool · 46 brand charts
Bike Size Calculator
Height and inseam in, a starting frame size out. The answer comes from the published chart for your bike type and brand, then from the geometry of the exact model when you pick one.
- Height in cm or ft/in
- Inseam, measured or estimated
- Bike type, brand and model
What the result gives you
Recommended size
The label a published chart puts your measurements in.
Also consider
The next size up or down when the ranges overlap.
Height range check
Your height shown inside the range the chart covers.
Brand comparison
The same measurements checked against other brand charts.
- brands with official data
- 46
- models listed
- 297
- model size charts
- 23
- bike categories
- 5
Find your bike size
Three steps: measurements, bike, riding position.
Height and inseamPublished chartsNo sign-up
Measuring inseam
Bike inseam is measured from the floor to your crotch in a riding stance, not the inside leg of your pants. Being 2 cm out usually moves the answer by one size.
Your result
Your size appears here
Add your measurements and pick a bike type. The answer compares your height and inseam against published size ranges.
What you entered
- Height
- 5'10" (178 cm)
- Inseam
- 32 in (81 cm)
- Bike type
- Kids
- Brand
- Not sure
- Riding position
- Balanced
- A main size and the next size up or down
- Your height shown inside the chart's range
- The same measurements in other brand charts
Need measurements first? Read how to measure height and inseam.
Starter kit
Helmet, light, lock, bottle, and a pant-leg strap. Size the bike here; buy the complete adult bike at a shop.
NiteRider
Swift 300
Compact USB headlight for commuting and dusk rides.
Handlebar mount, 300 lumens
View on AmazonPrice and availability on Amazon
Kryptonite
Evolution Mini-7 with 4′ cable
Hardened U-lock plus a cable for wheels or a locked-together pair.
Fits most road, gravel, and hybrid frames
View on AmazonPrice and availability on Amazon
CamelBak
Podium Chill 21 oz
Insulated squeeze bottle for everyday rides.
Fits a standard ~73 mm cage
View on AmazonPrice and availability on Amazon
Green Guru
Narrow pant-leg strap
Upcycled inner-tube strap that keeps a pant leg off the chain.
Adjustable hook-and-loop, about 16 in long
View on AmazonPrice and availability on Amazon
As an Amazon Associate we earn from qualifying purchases. Affiliate disclosure.
How the answer is built
Height sets the range. Inseam and geometry explain the fit.
Every answer names the chart it came from and the numbers that decided it.
Official chart ranges
Every recommendation starts from the height range the brand publishes, not a rule of thumb.
Bike type and labels
Road, gravel, mountain, hybrid and kids frames use different labels for the same rider.
Brand and model labels
178 cm can be a 54, a 56 or an M/L depending on which chart you are reading.
Inseam and standover
Inseam confirms clearance and decides the tie when two size ranges cover your height.
Stack and reach
Front-end height and handlebar reach explain how the finished fit will feel.
Sizing up or down
Riding position decides whether to size up for comfort or down for control.
Before you calculate
Measure once, calculate once.
Two numbers make the recommendation useful. Everything else is optional.
- 01
Height without shoes
Stand tall against a wall and mark the crown of your head. Height sets the first size range.
- 02
Inseam in a riding stance
Floor to crotch, not the inside leg of your pants. Inseam confirms clearance and standover.
- 03
No inseam? Estimate it
Turn on the estimate switch and the calculator works out your inseam from height, then marks the answer as an estimate.
Measuring in feet and inches? The calculator converts both ways, so 5'10" and 178 cm return the same size.Full measurement guide
Height
Stand against a wall without shoes, look straight ahead, and mark the crown of your head. Measure floor to mark in centimeters, then keep the number to the nearest half centimeter.
Inseam
Bike inseam is floor to crotch in a riding stance, not the tag inside your pants. Straddle a broomstick, lift it until it sits firmly, and measure the stick's height from the floor.
Next step
Take the answer to the chart.
Once you have a size, open the chart for your bike type or brand and confirm the label before you buy.
Road
Centimeter labels
Covers 5'1"–6'6" in rider height.
Open chartGravel
Letter and cm labels
Covers 5'1"–6'6" in rider height.
Open chartMountain
Frame and wheel sizes
Covers 4'11"–6'8" in rider height.
Open chartKids
Wheel sizes
Covers 2'11"–5'3" in rider height.
Open chartHybrid
Inches and letters
Covers 4'10"–6'6" in rider height.
Open chartBefore you buy
A size is a shortlist. Four checks make it a purchase.
The calculator returns one size and the runner-up. These are the numbers that separate the two on the frame you are actually buying.
01Standover clearance
Stand flat-footed over the top tube. If the frame touches you, that size is too tall no matter what the chart says.
02Stack and reach
Compare front-end height and handlebar reach on the model you are buying, not against another brand's label.
03The chart for the right year
Brands refresh geometry by model year, so confirm the table that matches the bike in front of you.
04A test ride or a fit
Twenty minutes on the frame beats any size chart on paper. A fitter can adjust the last few millimeters after purchase.
FAQ
Calculator questions, answered.
Short answers for riders who already have a number and want to sanity-check it.
Can I calculate bike size without inseam?
Yes. Turn on the inseam estimate and the calculator works it out from your height. If standover clearance matters, measure your real inseam before you buy.
How accurate is the calculator result?
It narrows the size ranges a brand publishes; it cannot feel the bike for you. Test ride the frame, or book a bike fit, when you are between two sizes or comparing two models.
Why do brand and model matter?
Brands use different labels and geometry. A medium road bike from one brand can overlap with a 54 or M/L from another, so the answer changes when you switch brand or bike type.
What should I check after the calculator result?
Confirm standover, stack, reach, and the brand's published chart for the exact model and year you plan to buy. Those numbers decide the fit once two sizes both look right.
Is the calculator free to use?
Yes. No account, no email, no payment. The answer stays on screen while you change bike type, brand or riding position.
Change one answer, watch the size move.
Switch the bike type, brand or riding position and the answer changes with it. When two sizes are close, clearance and your riding position decide which one to take.