Floss Rule Words List + Free Worksheet (FLSZ Rule)

The floss rule (also called the FLSZ rule) is a phonics spelling rule. Right after a short vowel at the end of a one-syllable word, the sounds /f/, /l/, /s/ and /z/ are usually spelled ff, ll, ss and zz, as in puff, hill, mess and buzz. Words that follow it are called floss words, and floss is one of them. Some schools call the extra letter a bonus letter.

If your child writes “hil” for hill, the miss is in spelling. Two letters make one sound. Children read ff, ll and ss early. The spelling rule usually comes at the end of kindergarten or the start of 1st grade, after CVC words. You can print our free floss rule worksheet. No signup, no email.

What is the floss rule? Three checks

Double the last letter when every answer below is yes.

1. Is it one syllable? bell is. rabbit isn’t.
2. Is the vowel short? pass is. seal isn’t.
3. Does /f/, /l/, /s/ or /z/ come right after the vowel? In hill it does.

Floss rule examples: puff, hill, mess and buzz meet all three checks, so each gets a double consonant at the end of the word.

These stay with one letter:

• elf, self, golf: an l comes before the /f/, making an ending blend.
• peel, seal, snail, roof: not a short vowel.
• pile: the e makes the i long (magic e). Compare pill.

Try is next. It passes all three, so the rule would spell it “izz.” It’s a rule breaker.

The floss spelling rule is about writing words. For reading, the two letters make one sound. Map hill in three sound boxes: h, i, ll. Our letter tiles include gold ff, ll, ss and zz tiles, used for blending. The ck in duck works the same way. Two letters make one sound. And ss and ll are doubled letters, not digraphs.

Why is it called the floss rule? FLSZ, FLoSS and bonus letters

Floss carries f, l and s, and it follows its own rule. Some programs add z: FLoSS(Z), FLSZ, FSZL, or the flossy or fizzle rule. Others say the ff, ll, ss, zz rule.

A doubled last consonant in Middle English marked a short vowel.

Floss rule words list: ff, ll, ss, zz

Page 1 of the free PDF.

This floss words list opens with short, CVC-shaped words. Blends come next, then digraphs (after sh, ch, th and wh). We’ve left out words that aren’t kid-friendly.

-ff words

• Short words: off, puff, cuff, huff
• With blends: staff, cliff, sniff, stiff, stuff, fluff, gruff, bluff
• With digraphs: whiff

-ll words

• Short words: hill, fill, will, pill, bill, mill, ill, dill, doll, bell, fell, sell, tell, well, yell, dull, gull, hull
• With blends: still, spill, drill, grill, skill, frill, spell, smell, swell, skull
• With digraphs: chill, shell, thrill, shrill

-ss words

• Short words: pass, mass, hiss, kiss, miss, boss, moss, toss, loss, less, mess, fuss
• With blends: class, grass, glass, brass, floss, cross, dress, press, bless
• With digraphs: chess

-zz words

• Short words: jazz, fizz, buzz, fuzz
• With blends: frizz

Floss words by vowel

No everyday kid word ends in -eff, -ezz or -ozz.

	short a	short i	short o	short e	short u
ff	staff (blend)	cliff, sniff (blends)	off	none	puff, cuff, huff
ll	none early	hill, fill, will	doll	bell, tell, yell	dull, gull, hull
ss	pass, mass	hiss, kiss, miss	boss, moss, toss	less, mess	fuss
zz	jazz	fizz	none	none	buzz, fuzz

Doll, ball and roll all end in ll, but only doll keeps a short vowel

doll, dull, gull, hull and skull keep a plain short vowel. Those are floss words.

ball, call, roll, troll, full, pull and bull double their l too, yet they break check 2. The vowel changes. The a in ball says /aw/ (or /ah/ in some accents), roll has a long o, and full has the /oo/ of book. Teach them as chunks. Until then, all (whole word) is a heart word.

shall has a short a, so it is a real floss word. A child who knows ball may read it as “shawl,” so it gets a heart: shall (a).

Chunk practice: ball in the hall, a tall wall and a bull can roll.

Floss rule exceptions: words that don’t follow it

Only some of these count as heart words.

• is, as, has, his: by the rule they’d end in zz, but they keep one s, and it says /z/. Heart words: is (s), as (s), has (s), his (s).
• was, of, have: odd spellings. In was (a, s), the a says /u/ and the one s says /z/. The word of (whole word) ends in /v/. Pair it with off, a real floss word. have ends in an e, not a second v.
• if, yes, us, bus, gas, plus, pal: your child reads them fine. No heart. The one letter only matters for spelling. This joins them once th is taught.
• quiz: just one z, the least reliable floss letter.
• add, egg, odd, inn: d, g and n aren’t floss letters. Little words like in can be two letters; other words usually get a third (inn).

When is the floss rule taught?

Reading comes first, and ff, ll and ss are group 4 of our letter-sound order, with ck in group 3. The spelling rule comes once all five short vowels and CVC words are solid, usually at the end of kindergarten or the start of 1st grade. Next come the ll chunks and digraphs, well before magic e. See what comes after CVC words.

In UFLI Foundations it is lesson 42, and -all, -oll, -ull follow in lesson 43 (see our worksheets in UFLI order).

Practicing the floss rule at home in 5 minutes

Say the three checks out loud on hill. One syllable, short i, /l/ right after it. Three yeses, so double it. Then, one a day:

1. Word chain. Build hill with letter tiles, then change one sound at a time: fill, fell, bell, bill.
2. One letter or two? Say mess, puff or buzz. Your child writes the ending.
3. Floss or not? Say pairs: bus/fuss, elf/bell, his/hiss, of/off. Which one doubles?
4. Read a sentence:
   • The bell fell off the hill.
   • The bug will buzz in the sun.
   • Kim will kiss his doll.
   • Tom did not miss the bus.

Free floss rule worksheet (ff, ll, ss, zz)

Our floss (FLSZ) rule worksheet is a free 3-page PDF:

• Page 1: the three checks, the four endings with example words and the rule breakers. Use it as an anchor chart or a poster.
• Page 2: the floss rule words list by stage, with check boxes.
• Page 3: dictation, a picture activity, the four sentences and an answer key.

It’s made to line up with lesson 42 of UFLI Foundations’ scope and sequence. Download the free floss rule worksheet. No signup, no email. More for this stage in our printables library.

Questions parents ask

What are floss words? Words that follow the floss rule: one syllable, a short vowel, then a doubled f, l, s or z (puff, hill, mess, buzz). Floss is one.

Is off a floss word? Yes. In many American accents, the o in off, boss and moss sounds a little like the aw in saw, but it still counts as short o. Don’t mix it up with of, which ends in /v/.

Why doesn’t bus follow the floss rule? bus (1832) is short for omnibus. yes, us and if are old everyday words, plus is Latin, pal came from Romani, and a Flemish chemist made up the word gas in the 1600s. And chef is French: its ch says /sh/.

Why doesn’t have end in two v’s? v isn’t a floss letter. English words almost never end in v, so an e goes on instead (have, give, live). The heart goes on the e: have (e).

Is the floss rule still used? Yes, for most short words that end in /f/, /l/ or /s/ after a short vowel. z is the weak letter: only a handful of words double it (buzz, fizz, fuzz, jazz), and about as many keep one letter (is, as, has, his, quiz).

Is z part of the floss rule? UFLI and Lexia include z. Fundations leaves it out, since z “does not always get doubled” (quiz). Teach it, but expect few words.

What are bonus letters? Fundations’ name for the doubled f, l or s. You hear one sound, so the extra letter is a bonus.

What grade is the floss rule taught? Usually at the end of kindergarten or the start of 1st grade, once CVC words are solid. Children read ff, ll and ss earlier. It’s lesson 42 in UFLI Foundations.

Does the floss rule work in longer words? It’s a one-syllable rule. Endings keep the double (fluffy, hissed, buzzed), but doubles inside rabbit or puzzle come from other patterns.

Is the floss rule the same as the doubling rule? No. The doubling rule is for adding endings (hop, hopping) and comes after magic e. The floss rule is about how a short word ends.

The same short-vowel words show up in our reading games, with no ads and no Wi-Fi needed. Next: the ball, roll and pull chunks, then digraphs.

Lesson numbers are cited for alignment only. This post and its PDF are our own original work, not created by nor endorsed by UFLI or the University of Florida.