Towing Capacity Calculator

Check whether a trailer or caravan is legal and safe to tow from the kerb weight, gross train weight, towball limit and trailer weight, against the noseweight limit and the 85% guideline.

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Input
Output

About towing capacity calculator

Towing Capacity Calculator does its work in front of you rather than sending anything away to be processed. What you see is the whole of it.

Because the work happens here, pasting production data carries no more risk than opening the file locally. Nothing is logged, since nothing arrives to log.

You will find it under Vehicles, alongside 1 other tool for the same sort of job.

Runs in this tab, so nothing you type is uploaded.

How to use it

01
Start it
Every control is on the tool itself. Keyboard shortcuts, where there are any, are listed beside it.
02
Watch it run
It updates in the page as you go. Nothing is sent anywhere, so it keeps working with the network off.
03
Close when done
Nothing is stored between visits. Reloading gives you a clean start rather than picking up where you left off.

Examples

A 1,600kg car towing a 1,300kg trailer
3,800kg gross train weight, a 100kg towball limit, 80kg measured noseweight
Input
kerbWeightKg: 1600
grossTrainWeightKg: 3800
towballLimitKg: 100
trailerActualWeightKg: 1300
trailerNoseweightKg: 80
Output
Legal max trailer weight kg: 2200
Recommended max trailer weight kg: 1360
Noseweight percent of trailer weight: 6.15
Trailer within legal limit: yes
Trailer within towball limit: yes
Trailer within85 percent guideline: yes
Overall safe to tow: yes

Questions

Does Towing Capacity Calculator work offline?+

Yes. It is JavaScript running in this tab, so once the page has loaded it needs nothing further from the network. Put the machine in flight mode and it carries on. Nothing you do here is sent anywhere, because there is nowhere for it to go.

Does it remember anything between visits?+

No. Reload the page and it starts from nothing. There is no account, no saved state and no cookie holding your last session. That is a deliberate trade: it cannot lose your data because it never keeps any.

Is it accurate?+

Timing comes from performance.now(), the high resolution clock the browser provides, rather than from setInterval, which drifts by a few milliseconds every tick and compounds over minutes. What can still shift things is the browser throttling a tab in the background, so leave it visible if the timing matters.

Does it make a sound?+

Where a sound makes sense, it is generated with the Web Audio API rather than loaded as a file, so there is nothing to download and nothing to block. Browsers refuse to start audio until you have interacted with the page, which is why the first press is what switches it on.

Can I use Towing Capacity Calculator on a phone?+

Yes. The controls are sized for touch and the layout collapses to one column on a narrow screen. Bear in mind that a phone locking its screen will suspend the page, and timing stops with it.