An estimated £266 billion worth of household possessions across the UK are not insured against risks such as theft, fire, flooding and accidental damage, according to insurers.
The calculations were made by the Association of British Insurers (ABI), which said the average UK household contains £35,000 worth of possessions.
The ABI said the typical contents of a home are worth more than the average annual salary, which stands at £27,000.
The total value of possessions owned by all UK households are now worth an estimated £950 billion - which is more than the combined value of all homes in Scotland, Wales and Northern Ireland, at £630 billion, the ABI said.
But more than a quarter (28%) of households do not have home contents insurance - meaning around £266 billion worth of possessions could be at risk according to the ABI, which based its calculations on the Office for National Statistics' Wealth and Assets Survey.
The ABI said the average cost of home contents insurance, at £141 a year, works out at less than £3 a week, with combined buildings and contents policies costing under £6 per week typically.
The figures will feature in an ABI report released during its annual conference on February 27.
Mark Shepherd, head of property at the ABI, said it can be easy for people to underestimate the worth of all their household gadgets and other contents.
He continued: "With a wide variety of policies available, including no-frills policies tailored to people on limited budgets, insuring your possessions can mean that if the worst happens you are not left counting the cost for years to come."
Mr Shepherd said people should ensure that when their policy is due for renewal they review the value of their possessions to make sure they are adequately covered.