Discovery BoxExodus 30:13 
Context30:13 Everyone who crosses over to those who are numbered 1 is to pay this: a half shekel 2 according to the shekel of the sanctuary 3 (a shekel weighs twenty gerahs). The half shekel is to be an offering 4 to the Lord.
Exodus 38:26
Context38:26 one beka per person, that is, a half shekel, 5 according to the sanctuary shekel, for everyone who crossed over to those numbered, from twenty years old or older, 6 603,550 in all. 7
1 sn Each man was to pass in front of the counting officer and join those already counted on the other side.
2 sn The half shekel weight of silver would be about one-fifth of an ounce (6 grams).
3 sn It appears that some standard is in view for the amount of a shekel weight. The sanctuary shekel is sometimes considered to be twice the value of the ordinary shekel. The “gerah,” also of uncertain meaning, was mentioned as a reference point for the ancient reader to understand the value of the required payment. It may also be that the expression meant “a sacred shekel” and looked at the purpose more – a shekel for sanctuary dues. This would mean that the standard of the shekel weight was set because it was the traditional amount of sacred dues (S. R. Driver, Exodus, 333). “Though there is no certainty, the shekel is said to weigh about 11,5 grams…Whether an official standard is meant [by ‘sanctuary shekel’] or whether the sanctuary shekel had a different weight than the ‘ordinary’ shekel is not known” (C. Houtman, Exodus, 3:181).
4 tn Or “contribution” (תְּרוּמָה, tÿrumah).
5 sn The weight would be about half an ounce.
6 tn Heb “upward.”
7 tn The phrase “in all” has been supplied.
