Caravan Towing Weight Calculator: MTPLM, Tow Ball and the 85 Percent Rule
Every country gave the same idea a different acronym, and the result is a generation of caravanners squinting at a compliance plate wondering whether MIRO and Tare are the same thing. They are. This calculator speaks every dialect: it builds your caravan's real loaded weight from the plate figure plus water, gas, battery and gear, solves your tow ball weight, and checks it against the 85 percent stability ratio that separates a relaxed tow from a white-knuckle one.
Caravan towing weight calculator
Caravan & Vehicle Setup
Water, gas and battery (1 L ≈ 1 kg)
Tow Verdict
Plate figures ready?
Enter your vehicle and caravan plate weights, fill in what's loaded inside, then tap Calculate Caravan Towing. The 85 percent ratio, tow ball weight and GTM all run together.
7-point safety check
Standards applied
- Tow rating:
SAE J2807 - Hitch & coupling:
SAE J684,ISO 1103 - Trailer electrics:
ISO 11992,ISO 1724 - Trailer braking:
FMVSS 121(US),ADR 38(AU),C&U Regs(UK) - Caravan plate labelling:
EU Whole Vehicle Type Approval
Why caravanning has more acronyms than a government form
Stand a British caravanner, an Australian caravanner and an American RV owner in the same room and ask them to describe their empty caravan weight, and you will get three different acronyms for the identical concept. MIRO in the UK and Ireland. Tare in Australia and New Zealand. Curb weight in North America. The plate on the caravan says one thing, the forum thread says another, and somewhere in the confusion a perfectly good caravan gets towed 40 kg over its limit because nobody realised MTPLM and ATM were the same idea with different passports.
This calculator does not pick a single country's vocabulary and force everyone else to translate. It detects your country, switches the labels to match your compliance plate, and runs the maths underneath identically regardless of what the field happens to be called. Add the water tank, the gas bottles, the leisure battery and the gear that always somehow weighs more than anyone estimated, and the calculator builds your true loaded weight, then checks it against both your caravan's own limit and the more conservative 85 percent stability ratio relative to your tow vehicle.
Terminology that follows you
MIRO, Tare, GVWR; MTPLM, ATM, ATM. The labels switch with your country selection, the physics underneath never changes.
Payload builder
Water, waste, gas, battery, awning and gear added piece by piece, the way the weight actually accumulates in real life.
85% stability ratio
The Caravan and Motorhome Club guideline, computed live against your specific vehicle kerb weight, not a generic rule of thumb.
GTM separate from ATM
A caravan can be under its ATM and still overload its own axles. This calculator checks both independently.
The same numbers, six different names
This is the decoder ring. Whatever your compliance plate calls it, here is what it actually means and where the equivalent term lives in other countries.
| Concept | UK / Ireland | Australia / NZ | North America | EU |
|---|---|---|---|---|
| Empty caravan weight | MIRO | Tare | Dry / Shipping weight | Mass in running order |
| Max loaded caravan weight | MTPLM | ATM | GVWR | Technically Permissible Mass |
| Max axle-only weight | GTM (rarely shown) | GTM | GAWR | Technical axle mass |
| Tow ball / hitch weight | Noseweight | Tow ball mass | Tongue weight | Vertical coupling load |
| Empty vehicle weight | Kerb weight | Kerb mass | Curb weight | Mass in running order |
| Max loaded vehicle weight | GVW | GVM | GVWR | Technically Permissible Mass |
How to use the caravan towing weight calculator
Two compliance plates and four minutes. The vehicle plate and the caravan plate hold every figure you need to start.
Pick vehicle
Country, brand and model fill the tow rating, kerb weight and GVWR.
Caravan plate
MIRO/Tare and MTPLM/ATM from the plate near the entry door.
Build payload
Water, gas, battery, awning, gear. Watch the loaded weight grow.
Tow ball weight
Measured or estimated. Checked against the 85% rule and noseweight limit.
Read verdict
7 checks, stability ratio, GTM, and a cost per km estimate.
Tow vehicles built into the database
The cars, SUVs and pickups that actually pull caravans worldwide, from family wagons to heavy duty trucks.
Methodology: how the maths are actually done
Loaded caravan weight
MIRO/Tare plus every payload item entered: water, waste, gas, battery, awning and personal gear, all at 1 litre = 1 kg for liquids. Checked against MTPLM/ATM as the absolute ceiling.
Tow ball weight estimate
When not measured, estimated at 7 to 10% of loaded caravan weight, the commonly cited rule of thumb, with the calculator defaulting to 8.5% for a balanced estimate. Always replace with a real measurement when possible.
85% stability ratio
Loaded caravan weight divided by tow vehicle kerb weight, expressed as a percentage. Below 85% is the conservative guideline; 85 to 100% is legal in most jurisdictions but requires more driving skill; above 100% is generally discouraged for new tow drivers.
GTM from ATM
GTM equals ATM minus tow ball weight. The axle check confirms this GTM figure stays under the caravan's own axle rating, a check that catches overloads ATM alone would miss.
SAE J2807 and ISO 1103
Tow rating methodology follows SAE J2807. Coupling ball and hitch compatibility follows ISO 1103 and SAE J684, applied identically regardless of whether your caravan calls it a coupling head or a hitch receiver.
Brake thresholds by country
Loaded against FMVSS 121 (US), ADR 38 (Australia, 750 kg) and UK Construction and Use Regulations (750 kg MAM). Caravans almost universally exceed these thresholds, so brakes are assumed standard equipment.
Every towing tool a caravan owner actually needs
This calculator gets your loaded weight and stability ratio right. These tools handle the rest of the caravanning picture.
Heaviest caravan your vehicle can pull
The reverse solver for true maximum trailer weight, useful before committing to a bigger van.
Cargo distribution and sway stability score
Models where weight sits inside the caravan and scores sway risk from cargo placement, separate from the plate-weight check above.
Correct cold PSI once loaded weight is known
Set the precise cold inflation for the caravan axle that matches your newly calculated loaded weight.
VIN lookup for exact tow vehicle specs
Decodes your 17-character VIN to retrieve the precise tow rating for your build, not the model-line headline.
Fifth wheel 8-limit safety analysis
For owners stepping up to a fifth wheel RV behind a heavy duty truck, the dedicated pin weight and axle check tool.
RV and camper pre-purchase matcher
For mixed fleets running both a caravan and a motorhome, this tool matches your vehicle to the right RV class before you buy.
Full caravan trip fuel and recovery bill
Enter the trip distance and get a line-by-line fuel and breakdown recovery cost estimate for the caravan and tow vehicle combination.
Ford F-Series and Ranger caravan towing by trim
Deep-dive into Ford configurations with trim-level payload figures the generic tables compress into one number.
Touring across a border? The legal weight rules and licence requirements change at every line on the map. The US FMCSA and state brake law calculator covers all 50 states for RV-style trailers. Australian caravanners chasing the four-limit GCM check should see the Australian ATM, GCM and tow ball mass calculator. UK tourers towing on a post-1997 car licence need the UK MTPLM and B+E licence entitlement checker. Canadian snowbirds planning a long tow should check the Canadian provincial towing weights and winter rules guide. The complete picture of every tool on the site is at the global towing safety resource hub.
Frequently asked questions
What is the difference between MTPLM and ATM?
They describe the same measurement using different regional terminology. MTPLM, Maximum Technically Permissible Laden Mass, is the term used across the UK and Europe. ATM, Aggregate Trailer Mass, is the Australian and New Zealand equivalent. North American caravans typically label the same concept GVWR. All three sit on the caravan's compliance plate and represent the absolute maximum the loaded caravan, including tow ball weight, may legally weigh.
What is the 85 percent rule and is it law?
It is a widely cited stability guideline, not a legal requirement in most countries. The recommendation, popularised by caravan and motorhome clubs, is that a loaded caravan should weigh no more than 85 percent of the tow vehicle's kerb weight, particularly for newer or less experienced tow drivers. A caravan at 100 percent of the vehicle's weight is towable and legal in most jurisdictions, but the lighter ratio meaningfully reduces snaking and sway risk, especially on motorway speeds and in crosswinds.
This calculator computes your specific ratio and flags it as a caution rather than a hard failure when it sits between 85 and 100 percent, since the legal limit and the prudent limit are genuinely different numbers.
How do I calculate tow ball weight without a scale?
A dedicated tow ball weight scale is the most accurate method, and a reasonably cheap accessory considering what it protects against. Failing that, household bathroom scales with a length of timber as a lever arrangement can approximate it, though with less precision. As a planning estimate before you have either, tow ball weight typically falls between 7 and 10 percent of the loaded caravan's total weight. This calculator uses 8.5 percent as a working default when you have not yet measured the real figure, then flags it as an estimate rather than a confirmed number.
What is GTM and why check it separately from ATM?
GTM, Gross Trailer Mass, is the maximum weight the caravan's own axles are permitted to carry, deliberately excluding the tow ball weight that the vehicle carries instead. The relationship is GTM equals ATM minus tow ball weight. Checking it matters because a caravan can sit comfortably under its ATM while still overloading its own axles, if the tow ball weight happens to be unusually low for that particular load distribution. This calculator runs GTM as an independent check rather than assuming an ATM pass means the axles are automatically fine.
Does water in the tank really count toward my towing weight?
Yes, and it is one of the most commonly forgotten weight items because it is invisible once the tank cap is closed. Fresh water weighs approximately 1 kilogram per litre, so a full 100 litre tank adds 100 kg on its own. Add waste water, a full gas bottle or two, and a leisure battery, and you have easily added 150 to 200 kg before a single piece of clothing goes in. Many experienced caravanners deliberately travel with partially filled tanks for exactly this reason, topping up closer to the destination rather than carrying a full tank the whole way.