She gleaned therefore in the field till evening: and beating out with a rod and threshing what she had gleaned, she found about the measure of an ephi of barley, that is, three bushels:

And she gleaneth in the field till the evening, and beateth out that which she hath gleaned, and it is about an ephah of barley;

So she went on getting together the heads of grain till evening; and after crushing out the seed it came to about an ephah of grain.

And so she gathered in the field until evening. And striking and threshing with a staff what she had gathered, she found about the measure of an ephah of barley, that is, three measures.

And beat out that she had gleaned - Namely, with a stick, as the word implies (compare Deuteronomy 24:20; Isaiah 27:12). This method is still commonly practiced. Ruth gleaned enough to support herself and her mother-in-law for five days Exodus 16:16.

An ephah of barley - Not less than seven gallons and a half; a good day's work. On Hebrew measures of capacity, see the note on Exodus 16:16.

So she gleaned in the field until even,.... An instance of her great diligence and industry, attending to this mean employment constantly from morning tonight:
and beat out that she had gleaned: she did not bind up her gleanings in a bundle, and carry it home on her head, as gleaners with us do, but she beat it out with a staff in the field, where she gleaned it, and winnowed it, very probably in the threshingfloor of Boaz; by which means what she had gleaned was brought into a lesser size and weight, and was a lighter burden to carry home:
and it was an ephah of barley; or three seahs of barley, as the Targum; which, according to Bishop Cumberland (i), was six gallons, and three pints, and three solid inches: an omer is said to be the tenth part of an ephah, and, made into bread, was as much as a man could eat in one day, Exodus 16:16, so that Ruth got enough in one day, for herself and her mother-in-law, which would last five days at least. This was a great deal for one woman to pick up, ear by ear, in one day; and must be accounted for, not only by her diligence and industry, but by the favour shown her by the reapers, under the direction of Boaz, who suffered her to glean among the sheaves, and let fall handfuls for her to pick up.
(i) Of Scripture Weights and Measures, ch. 3. p. 64.

It encourages industry, that in all labour, even that of gleaning, there is profit. Ruth was pleased with what she gained by her own industry, and was careful to secure it. Let us thus take care that we lose not those things which we have wrought, which we have gained for our souls' good, 2-John 1:8. Parents should examine their children, as Naomi did, not to frighten or discourage them, so as to make them hate home, or tempt them to tell a lie; but to commend them if they have done well, and with mildness to reprove and caution them if they have done otherwise. It is a good question for us to ask ourselves every night, Where have I gleaned to-day? What improvement have I made in knowledge and grace? What have I done that will turn to a good account? When the Lord deals bountifully with us, let us not be found in any other field, nor seeking for happiness and satisfaction in the creature. We lose Divine favours, if we slight them. Ruth dutifully observed her mother's directions. And when the harvest was ended, she kept her aged mother company at home. Dinah went out to see the daughters of the land; her vanity ended in disgrace, Genesis 34. Ruth kept at home, and helped to maintain her mother, and went out on no other errand than to get provision for her; her humility and industry ended in preferment.

and beat out that she had gleaned--When the quantity of grain was small, it was beat out by means of a stick.
an ephah--supposed to contain about a bushel.

Thus Ruth gleaned till the evening in the field; and when she knocked out the ears, she had about an ephah (about 20-25 lbs.) of barley.

An Ephah - About a bushel.