A caravan towing weight calculator is an essential digital tool designed to help drivers determine if their vehicle can safely and legally tow a specific caravan or trailer. Unlike simple arithmetic, towing involves complex physics and legal regulations that vary based on vehicle weight, driver licensing, and manufacturer specifications.
This calculator specifically focuses on the relationship between the tow car's mass and the caravan's loaded weight. It is widely used by caravanners to adhere to the "85% Rule," a vital industry guideline suggesting that a loaded caravan should ideally weigh no more than 85% of the tow car's kerb weight to ensure stability on the road.
Anyone planning to tow a trailer—from holiday makers to equine enthusiasts—should use a caravan towing weight calculator before purchasing a new caravan or hitching up for a trip. Failure to check these weights can result in dangerous "snaking" (instability), invalidated insurance, and police prosecution for overloading.
The Towing Formula and Mathematical Explanation
The core calculation used in a caravan towing weight calculator revolves around the "Towing Ratio." This percentage indicates how heavy the caravan is compared to the car towing it. A lower percentage generally implies greater stability, as the heavier car can better control the lighter caravan.
The Core Formula
Towing Ratio (%) = (Caravan MTPLM / Car Kerb Weight) × 100
Where:
Caravan MTPLM is the Maximum Technically Permissible Laden Mass (the max weight the caravan is legally allowed to weigh).
Car Kerb Weight is the weight of the car with standard equipment and a full tank of fuel, but without passengers or cargo.
Variable Definitions
Variable
Meaning
Unit
Typical Range
Kerb Weight
Mass of empty vehicle + fuel
kg
1200 – 2500 kg
MTPLM
Max legal weight of loaded caravan
kg
1000 – 2000 kg
GVM
Gross Vehicle Mass (Max car weight)
kg
1800 – 3500 kg
GTW
Gross Train Weight (Max combined)
kg
3000 – 6000 kg
Practical Examples (Real-World Use Cases)
To understand how the caravan towing weight calculator works in practice, let's look at two scenarios involving common family vehicles.
Example 1: The Safe Match (Beginner)
Scenario: A family is new to caravanning. They own a Ford Mondeo Estate and want to buy a 4-berth caravan.
Car Kerb Weight: 1,600 kg
Caravan MTPLM: 1,300 kg
Calculation: (1,300 ÷ 1,600) × 100 = 81.25%
Result: This is a perfect match. The ratio is well under 85%, offering excellent stability for a novice tower. The car is significantly heavier than the caravan, reducing the risk of the "tail wagging the dog."
Example 2: The Dangerous Mismatch
Scenario: A driver attempts to tow a large twin-axle caravan with a lighter compact SUV.
Car Kerb Weight: 1,350 kg
Caravan MTPLM: 1,500 kg
Calculation: (1,500 ÷ 1,350) × 100 = 111%
Result: This is highly dangerous. The caravan is heavier than the car. While the car might physically pull it, any instability or crosswind could cause the caravan to drag the car out of control. Most camping clubs prohibit this, and it may exceed the car's legal towing limit.
How to Use This Caravan Towing Weight Calculator
Follow these steps to get an accurate towing match assessment:
Find your Car's Weights: Check your V5C registration document or owner's manual for "Mass in Service" (Kerb Weight) and "Technical Permissible Maximum Towable Mass" (Towing Limit). Enter these in the first two fields.
Find your Caravan's Weights: Look for the weight plate near the door or on the chassis. Enter the MTPLM (Max weight) into the calculator.
Select Experience Level: If you have towed for less than a year or are infrequent, select "Novice." This sets a stricter safety threshold (85%).
Review Results: The calculator will display your percentage match. Green indicates a safe match, yellow requires caution (experienced drivers only), and red indicates a dangerous or illegal match.
Check Payloads: Review the "Car Payload Allowance" to see how much luggage and how many passengers you can carry in the car itself.
Key Factors That Affect Caravan Towing Weight Results
While a caravan towing weight calculator gives a crucial baseline, several dynamic factors influence real-world safety.
Noseweight: This is the downward force the caravan hitch applies to the car's towball. It should generally be 5-7% of the caravan's weight. Too little causes instability; too much lifts the car's front wheels, reducing steering traction.
Payload Distribution: How you load the caravan matters. Heavy items should be low and over the axle. Loading heavy items at the rear creates a pendulum effect, drastically increasing snake risk regardless of the weight ratio.
Car Suspension and Power: A car with stiff suspension and high torque (diesel engines) often tows better than a soft-sprung petrol vehicle, even if they have the same weight.
Tyre Pressures: Rear car tyres usually need higher pressure when towing to handle the extra noseweight and drag. Incorrect pressures invalidate the stability calculations.
Speed: Stability decreases as speed increases. A match that is stable at 50mph might become unstable at 60mph. The "85% rule" assumes a prudent driving speed.
Legal License Limits: Even if the car can physically tow the weight, your driving license might restrict you. In many regions, standard licenses restrict the combined Gross Train Weight (GTW) to 3,500kg unless an additional test is passed.
Frequently Asked Questions (FAQ)
Is the 85% rule a legal requirement?
No, the 85% rule is a guideline recommended by major caravan clubs and safety organizations. However, if you have an accident and were towing at 100%+ ratio, you could be prosecuted for "driving a vehicle in a dangerous condition."
Can I tow a caravan heavier than my car?
Legally, yes, provided the caravan weight does not exceed the manufacturer's stated "Max Towing Limit" and you have the correct license (e.g., B+E). However, it is strongly advised against for safety reasons.
What is the difference between MRO and MTPLM?
MRO (Mass in Running Order) is the empty weight of the caravan as it leaves the factory. MTPLM is the maximum it is allowed to weigh once you have added clothes, food, gas bottles, and equipment.
Does the calculator account for passengers?
The standard ratio calculation uses the car's empty Kerb Weight. However, adding passengers increases the car's weight, which technically improves the stability ratio, provided you do not exceed the Gross Vehicle Mass (GVM).
What happens if I exceed the Gross Train Weight (GTW)?
This is illegal. If the actual weight of your fully loaded car plus your fully loaded caravan exceeds the GTW stamped on your car's VIN plate, you can be fined and your insurance will be void.
How accurate is V5C registration data?
It is usually accurate, but aftermarket additions to a car (like a towbar, roof rack, or heavy sound system) reduce your available payload. The only way to be 100% sure is to use a weighbridge.
Does an automatic gearbox affect towing capacity?
Sometimes. In some vehicle models, the automatic version has a lower towing limit than the manual version due to gearbox cooling limitations. Always check the specific manual for your trim level.
What is the "Outfit Matching" service?
This is a professional service often offered by caravan clubs where they check your specific car and caravan combination against a database of real-world tests. Our caravan towing weight calculator provides a digital version of this assessment.
Related Tools and Internal Resources
Explore more of our tools to help you manage your vehicle finances and safety:
// Global Variables (using var as requested)
var inputKerb = document.getElementById('carKerbWeight');
var inputTowLimit = document.getElementById('carTowLimit');
var inputGVM = document.getElementById('carGVM');
var inputMTPLM = document.getElementById('caravanMTPLM');
var inputExp = document.getElementById('driverExp');
var resultRatio = document.getElementById('ratioResult');
var badge = document.getElementById('statusBadge');
var statusText = document.getElementById('statusText');
var limitCheck = document.getElementById('limitCheck');
var limitText = document.getElementById('limitText');
var carPayload = document.getElementById('carPayload');
var trainWeight = document.getElementById('trainWeight');
var breakdownTable = document.getElementById('breakdownTable');
// Canvas context
var canvas = document.getElementById('towChart');
var ctx = canvas.getContext('2d');
// Initialize calculator logic
function calculateTowing() {
var kerb = parseFloat(inputKerb.value);
var towLimit = parseFloat(inputTowLimit.value);
var gvm = parseFloat(inputGVM.value);
var mtplm = parseFloat(inputMTPLM.value);
var experience = inputExp.value;
// Validation for negative or empty logic
if (isNaN(kerb) || kerb 0 && mtplm > towLimit) {
isLegal = false;
}
if (!isLegal) {
status = "ILLEGAL MATCH";
statusClass = "status-red";
message = "Your caravan is heavier than the car's maximum towing limit. Do not tow.";
} else if (ratio > 100) {
status = "DANGEROUS";
statusClass = "status-red";
message = "The caravan is heavier than the car. This is highly unstable and not recommended.";
} else if (ratio > 85) {
if (experience === "beginner") {
status = "CAUTION (Advanced Only)";
statusClass = "status-yellow";
message = "As a beginner, you should aim for < 85%. This ratio is better suited for experienced towers.";
} else {
status = "ACCEPTABLE";
statusClass = "status-yellow";
message = "Ratio is between 85% and 100%. Acceptable for experienced drivers with careful loading.";
}
} else {
status = "PERFECT MATCH";
statusClass = "status-green";
message = "The caravan is significantly lighter than the car ( 0) {
var margin = towLimit – mtplm;
if (margin >= 0) {
limitCheck.innerText = margin + " kg under limit";
limitCheck.style.color = "var(–success-color)";
limitText.innerText = "Legal towing capacity: " + towLimit + " kg";
} else {
limitCheck.innerText = Math.abs(margin) + " kg OVER limit";
limitCheck.style.color = "var(–danger-color)";
limitText.innerText = "Exceeds capacity of " + towLimit + " kg";
}
} else {
limitCheck.innerText = "N/A";
}
// Car Payload
if (gvm > 0 && kerb > 0) {
var payload = gvm – kerb;
carPayload.innerText = payload + " kg";
} else {
carPayload.innerText = "—";
}
// Train Weight
if (gvm > 0 && mtplm > 0) {
var train = gvm + mtplm;
trainWeight.innerText = train + " kg";
} else {
trainWeight.innerText = "—";
}
// 4. Update Table
updateTable(kerb, mtplm, ratioFormatted, status, towLimit);
// 5. Draw Chart
drawChart(kerb, mtplm, towLimit);
}
function updateTable(kerb, mtplm, ratio, status, limit) {
var html = "";
// Row 1: Ratio
html += "
";
html += "
Towing Ratio
";
html += "
" + ratio + "
";
html += "
" + status + "
";
html += "
";
// Row 2: 85% Guideline
var guide85 = (kerb * 0.85).toFixed(0);
html += "
";
html += "
85% Guideline Weight
";
html += "
" + guide85 + " kg
";
html += "
" + (mtplm <= guide85 ? "Pass" : "Exceeded") + "
";
html += "
";
// Row 3: Legal Limit
if (limit > 0) {
html += "
";
html += "
Car Towing Limit
";
html += "
" + limit + " kg
";
html += "
" + (mtplm <= limit ? "Pass" : "Fail") + "
";
html += "
";
}
breakdownTable.innerHTML = html;
}
function drawChart(kerb, mtplm, towLimit) {
// Simple Canvas Bar Chart
var width = canvas.width = canvas.parentElement.offsetWidth;
var height = canvas.height = canvas.parentElement.offsetHeight;
ctx.clearRect(0, 0, width, height);
// Data preparation
var guide85 = kerb * 0.85;
// Determine scale: max value among variables
var maxValue = Math.max(kerb, mtplm, guide85);
if (towLimit > 0) maxValue = Math.max(maxValue, towLimit);
maxValue = maxValue * 1.2; // add 20% headroom
// Chart config
var barHeight = 40;
var gap = 30;
var startY = 50;
var startX = 150; // space for labels
var chartWidth = width – startX – 20;
// Helper to draw bar
function drawBar(label, value, color, yPos) {
var bWidth = (value / maxValue) * chartWidth;
// Label
ctx.fillStyle = "#333";
ctx.font = "14px Arial";
ctx.fillText(label, 10, yPos + 25);
// Bar
ctx.fillStyle = color;
ctx.fillRect(startX, yPos, bWidth, barHeight);
// Value text
ctx.fillStyle = "#000";
ctx.font = "bold 12px Arial";
ctx.fillText(Math.round(value) + " kg", startX + bWidth + 5, yPos + 25);
}
// 1. Car Kerb Weight (Baseline)
drawBar("Car Kerb Weight", kerb, "#004a99", startY);
// 2. 85% Guide
drawBar("85% Guideline", guide85, "#28a745", startY + barHeight + gap);
// 3. Current Caravan
var carColor = (mtplm > guide85) ? "#ffc107" : "#17a2b8";
if (towLimit > 0 && mtplm > towLimit) carColor = "#dc3545";
drawBar("Your Caravan", mtplm, carColor, startY + (barHeight + gap) * 2);
// 4. Tow Limit (Line)
if (towLimit > 0) {
var limitX = startX + (towLimit / maxValue) * chartWidth;
ctx.beginPath();
ctx.moveTo(limitX, startY – 10);
ctx.lineTo(limitX, startY + (barHeight + gap) * 3);
ctx.strokeStyle = "#dc3545";
ctx.lineWidth = 2;
ctx.setLineDash([5, 5]);
ctx.stroke();
ctx.setLineDash([]);
ctx.fillStyle = "#dc3545";
ctx.fillText("Max Limit", limitX – 30, startY – 15);
}
}
function resetCalculator() {
document.getElementById('carKerbWeight').value = "";
document.getElementById('carTowLimit').value = "";
document.getElementById('carGVM').value = "";
document.getElementById('caravanMTPLM').value = "";
document.getElementById('driverExp').value = "beginner";
document.getElementById('results-area').style.display = 'none';
}
function copyResults() {
var ratio = resultRatio.innerText;
var status = badge.innerText;
var mtplm = inputMTPLM.value;
var kerb = inputKerb.value;
var textToCopy = "Caravan Towing Check:\n";
textToCopy += "Car Kerb Weight: " + kerb + " kg\n";
textToCopy += "Caravan MTPLM: " + mtplm + " kg\n";
textToCopy += "Towing Ratio: " + ratio + "\n";
textToCopy += "Status: " + status + "\n";
textToCopy += "generated by Caravan Towing Weight Calculator";
var tempInput = document.createElement("textarea");
tempInput.value = textToCopy;
document.body.appendChild(tempInput);
tempInput.select();
document.execCommand("copy");
document.body.removeChild(tempInput);
var btn = document.querySelector('.btn-primary');
var originalText = btn.innerText;
btn.innerText = "Copied!";
setTimeout(function() {
btn.innerText = originalText;
}, 2000);
}
// Initial Trigger if values present (browser autofill)
window.onload = function() {
if(inputKerb.value !== "") calculateTowing();
// Responsive chart resize
window.addEventListener('resize', function(){
if(document.getElementById('results-area').style.display === 'block') {
calculateTowing();
}
});
};