So they gathered them all is literally “so they gathered,” with no expressed object. Most modern translations attempt in one way or another to indicate that the object is the pieces left over (of verse 12). It may be useful to render this first clause of verse 13 “So they gathered up all the pieces that had been left over.” It is also possible to translate “so they received back from the people all the pieces that were left over,” if one assumes that the food was gathered up in this manner (see comments on verse 12).

The size of the baskets referred to cannot be precisely determined. Elsewhere in the New Testament this word is used in Matthew 14.20; 16.9; Mark 6.43; 8.19; Luke 9.17. In Matthew 15.37; 16.10 and Mark 8.8,20, a different word for basket is used—the same word used of the basket in which Paul was lowered from the wall (Acts 9.25). These baskets were evidently fairly large. It is possible that the term in John 6.13 had a general meaning and was used for baskets of various sizes and shapes. In many receptor languages there is a term for a special type of basket used for carrying agricultural produce, and this word would be the one to use in this context.

Quoted with permission from Newman, Barclay M. and Nida, Eugene A. A Handbook on the Gospel of John. (UBS Handbook Series). New York: UBS, 1980. For this and other handbooks for translators see here .