Consumer New Zealand wants shoppers to get behind a campaign that defines exactly how free-range their eggs or roast chickens are.

The organisation's chief executive, Sue Chetwin, said more consumers were favouring "free-range" products, believing the animals had a better life.

However, there could be up to 10,000 chickens in free-range flocks producing eggs and some chicken meat flocks had almost 40,000 birds, Ms Chetwin said.

Large flocks limited the amount of freedom a bird had, she said.

Consumer New Zealand is calling for new standards that outline the size of the flock an egg or chicken has come from.

People can add their name to a list of supporters asking the government for change.

Ms Chetwin has collected flock size information for 41 free-range egg and chicken meat brands to help shoppers find out if the free-range products they buy meet their standards.