Enter each sidewall size
Use width, profile and rim size, such as 205/55R16. Add up to four sizes or choose a legacy size.
Free fitment tool
Tyre Size Calculator
Compare dimensions, rolling diameter and fitment changes before tyres are fitted.
Free to useNo account needed
First time comparing tyre sizes?See how to enter a sidewall size, compare diameter and read the fitment result.
Enter Tyre Sizes
Add a legacy, truck, agricultural or industrial size 100 sizes
Codes that cannot be typed as width, profile and rim: vintage numeric, US alphanumeric, metric rim, truck, agricultural and industrial.
Metric and imperial sizes such as 225/40R18 and 31/10.5R15 go straight into the boxes above.
Truck, agricultural and industrial sizes are shown for dimensions only.
Speedometer and WOF output is hidden for them, because neither applies to a tractor or a forklift tyre.
Sizes marked bias are cross ply and are not interchangeable with a radial of the same code.
Selected Sizes
Detailed specificationsDiameter, sidewall, circumference and size guide
Specifications
How to Read Tyre Sizes
Metric205 / 55 / R16
205mm width. Sidewall = 55% of 205mm (112.75mm). 16" rim
Imperial31 / 10.5 / R15
31" overall diameter. 10.5" width. 15" rim
No profile165 R13
Profile left off means an 82 series. Reads as 165/82R13, 600mm tall
Legacy7.00 R16
Not a width. Dimensions come from standards tables: 778mm tall, 202mm wide
Two tyres9.5 R15
One code, two tyres: the LT numeric at 825mm or the 9.5L-15 implement at 767mm. Check the sidewall
Visual Comparison
Front View
Enter sizes and click Calculate
Side View
Speedometer Impact
| Your speedo reads | Actual speed (T2) | Actual speed (T3) | Actual speed (T4) |
|---|
These figures show the effect of the tyre size change alone, assuming your speedometer was
calibrated for Tyre 1. They are not what your dash will read. Under the applicable standard
(UNECE R39, mirrored by ADR 18) a speedometer must never read below true speed and may
legally read up to 10% + 4 km/h high. That allowance is one-sided, so most speedometers
already over-read before any tyre change is considered.
Dimensions only for this size. Speedometer, WOF and replacement options are hidden
because a truck, agricultural or industrial tyre is in the comparison. None of those
outputs apply: there is no WOF check for a tractor tyre, and the speedometer table assumes
a car speedometer calibrated to tyre 1. The diameter, width and sidewall figures above are
the published standard dimensions and remain valid.
Preliminary NZ WOF Size Check
Potentially Suitable Alternatives
Potentially suitable alternatives, matched on overall diameter only. Diameter is one of several things that decide whether a size is legal and safe on your vehicle.
| Size | Diameter | Sidewall | Width | Rim |
|---|
This is a size comparison, not a compliance check. Whether a tyre is legal on your
vehicle also depends on rim width, load index, speed rating, matching across an axle,
clearance under lock and compression, and whether the change needs LVV certification. Confirm
with your fitter or a certifier before committing.
Sizes shown are within +/-5% overall diameter of Tyre 1.
Rim figures are the standard measuring rim and its permitted range, and are left blank
where the sizing standard does not cover that size.
Need a specific size? Get a quote
Powered by 
Help & guide
Compare tyre sizes with confidence.
Use the complete sidewall size and compare the result with the vehicle and wheel limits before fitting.
Compare the diameter
Look at overall diameter, circumference and the speedometer difference. Small changes still affect clearance and gearing.
Check the fitment result
The comparison explains the calculated change. Confirm wheel width, offset, load rating and physical clearance on the vehicle.
Know the limit
This calculator checks dimensions. It cannot see suspension, brakes, guards or certify a modification.