In that first attack Jonathan and his armor-bearer killed some twenty men in an area of about half an acre.
NIV
And that first slaughter which Jonathan and his armor-bearer made was about twenty men within about a half acre of land [which a yoke of oxen might plow].
AMP
And that first slaughter, which Jonathan and his armourbearer made, was about twenty men, within as it were an half acre of land, which a yoke of oxen might plow.
KJV