A cup is 8 floz. A regular mug is about 12 floz; a teacup is about 5 floz. Can you estimate from there, or do you have a measuring jug or a plastic container that's marked 4 floz or 125ml? If so,
Pre-heat oven to 180. Prepare a 2lb loaf tin either by greasing it and putting a strip of greaseproof paper across the bottom or by using a liner.
2 or 3 ripe bananas, in a bowl, mash by whisking with a hand mixer
Add ½ cup oil - not a strong-tasting one; I use sunflower
Add ½ cup sour cream/buttermilk/vanilla yoghurt/soured milk (that's milk with a squeeze of lemon juice), whatever's in the fridge
2 eggs
1 tsp vanilla essence
Mix well.
In a large bowl, mix
2 cups plain flour
1½ cups sugar; I use soft light brown
1½ tsp baking powder
¾ tsp bicarbonate of soda
Add the wet ingredients to the dry and stir well, making sure there are no pockets of dry ingredients. Dollop into the prepared tin and bake for 30 - 35 minutes, or until a skewer comes out clean.
Sometimes I use half plain flour and half wholemeal, or I add about half a cup of pecans. Sometimes I use about ¼ cup of cocoa and only 1¾ cups of flour, and add chocolate chips. Sometimes the bananas are bigger and sometimes they're smaller. It always works, it's easy, it tastes good and it keeps well.