What widows and orphans are and why they matter
A widow is the last line of a paragraph that contains only one or two words and is stranded at the top of the next page. An orphan is the first line of a paragraph stranded at the bottom of a page, or a very short paragraph that appears alone. Both are single lines that have lost their paragraph. The reader's eye, which has been tracking a block of text, suddenly sees a line by itself, then a page turn, then the next block. The line feels disconnected, not because the words are wrong, but because the line has lost its context.
The tool models the line where a paragraph will break for the words per line your interior uses. At 10 words per line, a 33-word paragraph is three full lines of 10 plus a last line of 3, which is safe. The same 33 words at 8 words per line is four full lines of 8 plus a last line of 1, which is a widow. The words never changed; the line length did, and the last line moved from safe to stranded.
Widows are more common in short paragraphs and in paragraphs that end with a short word. A paragraph that ends with "lightly" as a single word on the last line is a widow even though the paragraph is long, because the last line is short. A paragraph that ends with "where the pen had pressed lightly" as three words on the last line is safe, because the last line has enough words to feel like a line.
Orphans are most common as very short paragraphs. A paragraph of two words, as Go home, is a single line that will appear alone at the bottom or top of a page. It is not a widow in the strict sense, because it is not the last line of a longer paragraph, but it reads as an orphan because it is a line by itself. The tool flags very short paragraphs as orphan-like for that reason.
Why widows feel wrong to the reader
Widows feel wrong because the eye has been tracking a block, not a line. A paragraph is a block of 3 to 8 lines that the eye reads as a unit, with the last line as the closing edge. When the closing edge is a single word, the block's edge is a spike, not a line. The eye lands on the spike, then on the white space that follows, then on the next block. The spike breaks the rhythm that the rest of the book has taught the eye to expect.
Widows at the top of a page feel worse than widows in the middle of a page, because the page break adds white space after the spike. A paragraph that ends with a two-word last line in the middle of a page has 3 to 5 words of white space to its right, then the next paragraph begins below. A paragraph that ends with a two-word last line at the top of a page has the same two words, plus the top margin, plus the page break, plus the next paragraph. The isolation is greater, so the fix matters more.
Orphans feel wrong for the opposite reason. A very short paragraph that is a single line by itself looks like a heading that lost its body, or a body that lost its paragraph. The reader's eye, which has been tracking multi-line blocks, suddenly sees a single line alone with white space above and below. The line feels stranded, not because the words are wrong, but because the line has lost its paragraph.
The fix for both is to give the stranded line company. A last line with 3 to 5 words has company within the line. A very short paragraph merged with the next paragraph has company within the block. The tool flags the stranded case so you can give it company, not so you can change the type.
How the checker estimates lines
The checker does not paginate your file. It estimates lines from words per line, which is the average words per line in your interior at the chosen trim and font.
For a 6×9 with Garamond Premier Pro at 12 on 15.5, 9 to 11 words per line is typical. For a 5×8 at the same family and size, 8 to 9 is typical. For a 7×10 at 11 on 14, 11 to 13 is typical. The tool defaults to 10, which is the center for a 6×9 trade paperback. If your interior is set tighter, the words per line will be higher; if it is looser, the words per line will be lower. Count the average words per line in your typeset interior for the most accurate check.
From words per line, the checker divides the paragraph's word count by the words per line, ceiling to get lines, and checks the last line's word count. Total words modulo words per line is the last line's words, with the special case that a remainder of zero means a full line. A paragraph of 33 words at 10 per line is 3 full lines plus a last line of 3, safe. A paragraph of 32 words at 10 is 3 full lines plus a last line of 2, widow. A paragraph of 31 words at 10 is 3 full lines plus a last line of 1, widow.
The checker also checks first-line length for very short paragraphs. A paragraph of two words at 10 per line is one line of two words, which is not a widow by the last-line rule, but it will appear as a single line alone. The tool flags it as a possible orphan so you can see it.
The estimate is not pagination. Real pagination also depends on hyphenation, justification, and the actual line breaks the typesetting engine chooses, which vary with the words themselves. A paragraph that is safe at 10 words per line may still widow at 10.2 if the engine breaks a long word across lines. The tool's estimate is the planning check that catches the obvious cases before you paginate. The final proof is the facing-pages spread.
Worked examples with the line math shown
Note: the following examples are hypothetical and illustrative rather than a sourced case study.
A typical paragraph with no widow is the safe case. Paragraph: The morning light fell across the kitchen table where the letter had been left open, its crease still sharp from the envelope and the ink still dark where the pen had pressed lightly. Words per line 10. Word count is 33, so lines are ceiling of 33 over 10, or 4, with 10 plus 10 plus 10 plus 3. Last line has 3 words, so the verdict is pass with no widow or orphan. The metrics show words per line 10, paragraph 1 words 33 with 4 lines and last line 3 words, and risk none. The breakdown shows paragraph 1 as 33 words over 4 lines with the note no widow or orphan, last line has 3 words. The recommendation is to keep the text as is and to check widows in the full pagination with facing pages, not to fix the font.
A paragraph that ends with a single-word widow is the common fail. Paragraph: The morning light fell across the kitchen table where the letter had been left open, its crease still sharp from the envelope. Words per line 10. Word count is 22, so lines are ceiling of 22 over 10, or 3, with 10 plus 10 plus 2. Last line has 2 words, so the verdict is warning with widow risk on one paragraph. The metrics show paragraph 1 words 22 with 3 lines and last line 2 words, and risk widow. The breakdown shows paragraph 1 as 22 words over 3 lines with the note widow risk, last line has only 2 words on 3 lines. The recommendation is to add 2 to 3 words to the paragraph or to rephrase the last sentence so the last line has 3 to 5 words. Adding lightly to the end, as where the pen had pressed lightly, moves the last line from 2 to 3 and clears the warning.
A very short paragraph is the orphan-like case. Paragraph: Go home. Words per line 10. Word count is 2, so lines are 1, with 2 words on that single line. The tool flags it as a possible orphan because a very short paragraph may appear as an orphan. The metrics show paragraph 1 words 2 with 1 line and last line 2 words, and risk orphan. The breakdown shows very short paragraph, 2 words, may appear as orphan. The recommendation is to merge the short paragraph with the next paragraph or to expand it to at least 3 lines. A two-word paragraph that is dialogue can be merged with the following narrative paragraph; a two-word paragraph that is a section break should be set as a centered ornament, not as a paragraph.
An empty check shows the starting state. Paragraph 1 empty, Paragraph 2 empty, words per line 10. Word count is zero, lines zero, last line zero. The verdict is fail with the headline paste a paragraph to check. The metrics show words per line 10, paragraph 1 words zero with zero lines, and risk not applicable. The breakdown shows empty paragraph. The recommendation is to paste the paragraph text as it appears in the interior, line breaks removed, to check the flow.
The line as a unit and why two words is the edge
A line is not just words. It is the horizontal space the words occupy, and that space depends on the words themselves. A last line with two short words, as of the, occupies less horizontal space than a last line with two long words, as understanding. Both are two words, but the short pair leaves more white space to its right, so the stranded feeling is stronger. The tool counts words, not characters, so it treats both as widow risk when the count is one or two, which is the correct conservative check. A human check should also look at character length: a last line with a single long word, as understanding, is less stranded than a last line with a single short word, as it, because the long word occupies more of the line. The tool flags both, but the eye will forgive the long single word more easily.
The same logic applies to the first line of a paragraph. A first line that is a single short word, as A, at the bottom of a page is more stranded than a first line that is a single long word, as Nevertheless, but both are orphans by definition. The tool flags very short paragraphs as orphan-like without measuring first-line length, because the paragraph is the unit that is stranded, not just the line. A paragraph that is a single sentence of 8 to 12 words will be two lines at 10 words per line, with a last line of 2, so it will be flagged as a widow even though the paragraph itself is not very short. The flag is still correct, because the last line is the stranded unit.
Edge cases: very short, very long, and the second paragraph
Very short is fewer than three words on the first line. A paragraph of two words at 10 per line is one line of two words, which the tool flags as a possible orphan. The fix is not to add a word to the paragraph to make it three words, though that would clear the flag, but to consider whether the paragraph should exist. Dialogue of two words, as Go home, is often better merged with the attribution or the next paragraph. A single word as a paragraph, as Yes, is almost always an orphan and should be merged.
Very long is more than 200 words at 10 per line, or 20 lines. A very long paragraph at 10 per line is 20 lines, which will span more than one page. The widow check still applies to the last line, but the more important check is whether the paragraph should be broken. Long paragraphs are hard to read in print, especially at 6×9 where the line length is moderate. The tool does not flag long paragraphs as widows, because the last line may be safe, but the interior will be more readable if long paragraphs are broken at natural breaths.
The second paragraph is optional, but it is useful for comparing two versions of the same paragraph. Paste the original in Paragraph 1 and the revised in Paragraph 2, keep words per line the same, and see whether the last line moves from 2 to 4. The comparison is more reliable than remembering the previous count, and it shows whether the fix worked without repaginating the whole file.
Words per line that is off by one changes the verdict. A paragraph of 33 words at 10 per line is safe with a last line of 3, while the same 33 words at 11 per line is 3 full lines plus a last line of 0, which the tool treats as a full line of 11, safe as well. A paragraph of 32 words at 10 is widow with a last line of 2, while the same 32 words at 11 is 2 full lines plus a last line of 10, safe. One word per line of difference, which is the difference between 5.5×8.5 and 6×9, moves the last line. That is why the words per line you enter should be the average for the interior you will actually print, not a generic default.
How to use the tool in under two minutes
Paste the paragraph text as it appears in the interior, with line breaks removed, into Paragraph 1. The text should be the words, not the line breaks, because the tool estimates lines from words per line. Add a second paragraph in Paragraph 2 if you want to compare an original and a revision, or leave it blank.
Set words per line to the average for your interior at the chosen trim and font. Use 10 for 6×9 if unsure, 8 to 9 for 5×8, 11 to 13 for 7×10. If your interior is set tighter, the words per line will be higher; if it is looser, the words per line will be lower. Count the average words per line in your typeset interior for the most accurate check.
Read the risk. The tool counts words, estimates lines, and checks the last line length. The metrics show words per line, paragraph words, lines, last line words, and risk. The breakdown shows each paragraph with the note you matched or missed.
Fix the last line if it has 1 to 2 words. Add or rephrase 2 to 3 words so the last line has 3 to 5. Do not fix widows by changing the font. Fix the paragraph text so the last line is not stranded, then reflow the pages.
Reflow and verify. Do not change the font to fix one widow. Fix the paragraph, reflow the pages, and check facing pages. The widow may move to a different paragraph, which is normal. Fix the new location.
Common mistakes and how to avoid them
Fixing widows by changing the font or the margins is the most common. A tighter font or a narrower margin can move a widow from one paragraph to the next, but it will create a new widow elsewhere and will change the whole book, not just the widow. Fix the paragraph text so the last line is not stranded, then reflow the pages.
Checking only the last paragraph of the chapter is the second. Widows are most common in short paragraphs and in paragraphs that end with a short word, which can occur anywhere. Check the paragraphs you suspect are short, plus a random sample of 10 to 15 paragraphs across the interior. Widows are most common in short paragraphs and in paragraphs that end with a short word.
Forgetting to check facing pages is the third. A widow at the top of a right-hand page is more visible than a widow at the top of a left-hand page, because the reader's eye lands on the right-hand page first. Check facing pages, not single pages. The previewer will show facing pages if you export as spreads.
Adding manual line breaks to fix widows is the fourth. Manual breaks do not reflow when you add or remove a page, and they create inconsistent leading. Fix the paragraph text, not the line break. Let the typesetting engine choose the breaks.
Ignoring very short paragraphs is the fifth. A paragraph of two words will appear as a single line alone. It is not a widow in the strict sense, but it reads as an orphan. Merge it with the next paragraph or expand it to at least 3 lines. Dialogue of two words, as Go home, is often better merged with the attribution or the next paragraph.
Forgetting to re-paginate after fixing is the sixth. A fix that adds 2 words to one paragraph moves every subsequent line by 2 words, which may create a new widow elsewhere. Fix the flagged paragraph, reflow the pages, and check facing pages again. Widow fixing is iterative.
Expecting KDP to fix widows automatically is the seventh. KDP prints what you upload. The previewer will show widows if they exist, but it will not fix them. You must fix the text and re-export.
Final checks before you lock the file
Run the checker once with the paragraphs you plan to ship and once with a second version where the words per line is one higher or lower, to see whether the result is sensitive to the estimate. If a paragraph is safe at 10 words per line but widow at 9, the paragraph is borderline and should be fixed even though it passes at your current estimate.
Open the interior at 100% and at facing pages. At 100% the text should look even, with no single line stranded at the top of a page. At facing pages the gutter should be visibly wider than the outside on the interior pages, and the text block should look centered between the outside and the gutter, not pushed toward the spine.
Compare the interior file's title page to the cover's title string. The cover's title and the interior's title page should match exactly, including capitalization, and the copyright page should carry the same publisher string as the cover. A mismatch will be flagged in preflight even though the margins are correct.
Upload and verify live. In the interior previewer, check the page thumbnails for widows at the top of each page. The last line of any paragraph that is a single word at the top is a widow. Fix the paragraph, not the font, and re-export. When the next book in the series is formatted, reuse the same words-per-line estimate for the same trim and font rather than relying on memory that the last book was 10 words per line. The estimate is the variable that compounds; the content is the variable that varies.