Ten-year-old William found a giant egg weighing in at 121 grams when he went to check the family brood in Victoria's Central Highlands on Saturday morning.

This is about twice the size of his usual egg finds.

William has seen some big eggs from his hens - three or four have come close to 110g. He has been egg-amining them against an article in The Courier from January 2016 in which Creswick's Jane Varney reported a 110g egg from three-year-old Bluebell.

He was rapt to have finally cracked Ballarat's biggest chicken egg on known record.

To put into perspective, not-for-profit egg farmer advocates Australian Eggs lists the average weight for an extra-large egg as 60g, a jumbo is 68g and a king size is 73g.

Guinness World Records has a white leghorn hen from New Jersey in the United States laying the world's heaviest egg at 454g in February 1956. That egg was a double-yolk, double-sheller.

The Ballarat family was unsure which of their Hy-line hens laid their prize: neither Cecil, Waz, Cefa, Paisley or Myrtle were showing any signs of strain.

All five joined the family as chicks in April, amid a rise for backyard chook demands in lockdown. They have been laying for what William says has been "a good couple of months".

Their regular diet is chicken pellets and food scraps.

The family still finds the occasional soft shell in the mix, but the biggest factor intervening in monitoring the egg-size progress has been neighbourhood crows who boldly pinch eggs during the day.

The hens are otherwise relaxed and well-loved. They are known to cheekily sneek inside when no-one is watching to try and sit on the couch and they have direct access to play in the next-door neighbour's yard with more human friends.

As for the giant egg, William remains considering how he might eat it. Maybe scrambled. Maybe poached.

Ballarat's previous biggest egg was, on last reports, fated to be boiled up with toast soldiers.