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Campervan conversion

Van payload calculator

Subtracts the build, the water, the people and the gear from the plated maximum, and says what is left — before the furniture is screwed down rather than after somebody is weighed.

The question this answers: “The plate says 3,500kg. How much of that have I already used, and is there anything left for water and luggage?”

From the plate on the vehicle, not from a brochure.

From a public weighbridge, with a full fuel tank.

Furniture, insulation, water tanks, battery, everything not yet fitted.

A litre weighs a kilogram. This is often the heaviest single item.

Including the driver.

Bikes, boots, food, bedding, the awning.

Result

Payload available now
1400 kg
Plated maximum minus what the vehicle weighs today. Everything below has to fit inside this.
Estimated weight loaded
2890 kg
82.6% of the plated maximum of 3500kg.
Margin remaining
610 kg
What is left for the things you have not thought of. There are always some.
Show the working
  1. Payload available3500 kg plated − 2100 kg as weighed1400 kg
  2. Water70 l × 1 kg/l70 kg
  3. People2 × 75 kg150 kg
  4. Total loaded2100 + 450 build + 70 water + 150 people + 120 gear2890 kg
  5. Against the plate3500 − 2890610 kg

Payload available now: 1400 kg. Estimated weight loaded: 2890 kg. Margin remaining: 610 kg

How it works

Subtraction, done against the right numbers in the right order. Payload is the plated maximum minus what the vehicle actually weighs today; the build, the water at a kilogram per litre, the occupants and the gear come out of that. The output is the margin left over.

What it assumes

  • The current weight is a real weighbridge figure with a full fuel tank. A manufacturer kerb weight is a different number, usually optimistic, and often excludes the driver — which is why this is an input rather than a lookup.
  • Fresh water is one kilogram per litre. That is physics rather than a convention and is the one figure here not open to argument.
  • The build estimate is yours. Weighing components as you buy them and keeping a running total is the only way to make it accurate, and it is what the activity page recommends.

Where it stops being reliable

  • It says nothing about axle loading. A vehicle can be within its total plated mass and over its individual axle limits, which is a separate plate figure and a separate offence — heavy items behind the rear axle are the usual cause.
  • It cannot tell you what your conversion will weigh. That is the hard part and it is the input the tool depends on most.
  • Being under the plated mass is not the same as being safe or legal in every other respect. Tyres, load distribution and the licence category are separate questions.

Sources

Sources for this section

Runs entirely in your browser — nothing you type is sent anywhere. Last reviewed 2026-08-14. More on Campervan conversion.