Exodus 30:13-14

13Each one who crosses over to those already counted is to give a half shekel, That is, about 1/5 ounce or about 5.8 grams; also in verse 15 according to the sanctuary shekel, which weighs twenty gerahs. This half shekel is an offering to the LORD . 14All who cross over, those twenty years old or more, are to give an offering to the LORD .