Working out how much to buy
Meat and filleted fish
For meat and filleted fish, allow about 125 g per head, depending on appetites. So half a kilogram (500 g) will feed four. This is just over the old pound. Sausages weigh around 40-80 g each and although many packs still carry the awkward 454 g pack weight, they are increasingly sold in 400 g and 500 g packs with 6 - 10 bangers inside.
At the Deli counter
Instead of asking for a 'quarter' (4 oz), ask for 100 g (which is slightly under the old quarter). Prices will be marked per kg and per 100 g so it is easy for you to calculate how much you will be charged.
1 kg of 'old' boiling potatoes for mash, roasting, etc. is enough for 4-6 servings depending on appetites. A baking potato weighs about 250 g. 500 g sprouts, carrots, leeks etc. will feed 4-6 while 250 g mushrooms or tomatoes is enough for 6 portions.
Fruits are frequently sold by the piece or ready bagged in 1 kg bags. However, should you wish to buy loose apples, remember a large cooking apple is about 250 g (or 4 to the kilogram) and there are approximately 6 dessert apples to the kilogram. All soft fruits are sold in punnets of 150 g, 200 g or 250 g depending on the season and availability, except for strawberries, which still are sold in awkward 227 and 454 g punnets.
A pack of butter is 250 g (¼ kilogram). Yogurts, crème fraîche and soft cheeses are sold in 150 g and 200 g packages. Cream and milk are still in awkward 284 and 568 ml packs, although longlife, UHT, organic and speciality milks are sold in easy 500 ml and 1 litre sizes.
The sooner all produce weights are standardised to simple metric the better it will be for consumers using ingredients in recipes and comparing prices.