Vehicles & Transport calculator
What Towing Mirror Extension Do I Need?
Use your measurements for trailer/caravan width, tow vehicle width, and desired rearward view angle to find towing mirror extension.
Enter your measurements
To work out what towing mirror extension do i need, begin with trailer/caravan width, tow vehicle width, and desired rearward view angle. The calculator produces towing mirror extension from the measurements that actually control the result.
- Trailer/caravan width — Required
- Tow vehicle width — Required
- Desired rearward view angle — Required
- Driver eye to mirror lateral geometry — Optional
Towing mirror extension
Enter the measurements above to calculate towing mirror extension.
How the calculation works
V12 calculation: baseExtension=max(0,(trailerWidth-towVehicleWidth)/2); angularAllowance=mirrorDistanceFromDriver×tan(toRadians(requiredViewAngle)) when mirrorDistanceFromDriver is supplied; minimumEachSideExtension=baseExtension+angularAllowance. Angle inputs are explicitly converted to radians before trigonometric functions where required.
Worked example
Example: Trailer/caravan width = 230 cm; Tow vehicle width = 185 cm; Desired rearward view angle = 5 °; Driver eye to mirror lateral geometry = 80 cm. Result: Minimum Each Side Extension = 29.5 cm; Angular Allowance = 0.07; Base Extension = 22.5 cm.
Before you decide
The result is only as accurate as the measurements entered. This page calculates the stated geometry or quantity only; product-specific construction or installation details can still affect the final choice. For what towing mirror extension do i need, the limiting result on this page is towing mirror extension.
Direct measurement/geometry calculation. No external reference is required for the arithmetic itself; the result is derived only from the user-entered measurements and the formula stored in calculationLogicJson.
Frequently asked questions
What does the Towing Mirror Extension calculator tell me?
It returns towing mirror extension from the measurements entered on this page. The calculation is specific to towing mirror extension, so the result should be compared with the exact product or specification you are considering.
Which measurements should I take for towing mirror extension?
Measure trailer/caravan width, tow vehicle width, desired rearward view angle, driver eye to mirror lateral geometry. Use clear, usable dimensions rather than nominal room or product labels.
Should I round the towing mirror extension?
Keep the calculated value for comparison, then choose a real product that meets or stays within the returned towing mirror extension while allowing for the clearances, tolerances or ratings shown by its manufacturer.