Depends on the radish you are growing, most are round and about half the size of a golfball - maybe a teaspoon full? Some are long and more like a 3" or 4" carrot. You will need to cut your gallon jug just below the handle so you can use the top as a 'greenhouse' effect. You really don't want to watch the radish grow as light isn't good for the root. It will pop up above the surface of the soil as it matures so you will see the size of your radish. Look for 'dtm' (days to maturity) as this tells you how long from first true leaf til harvest.
