Cat Vocal Folds: 10-15 mm, 2 Registers, 3 Hoarse Causes

A cat's voice comes from 2 folds of tissue 10 to 15 mm long, and nearly every hoarse cat lands in 3 groups: swelling, nerve failure, or a mass on one fold. Length and tension set the pitch, which is why the sounds at home split into 2 frequency classes, a 20 to 30 Hz purr and a 300 to 900 Hz meow. The useful first question is how many days the voice has been off, not how odd it sounds.

Two folds, 10 to 15 mm, 5 layers

The larynx is a 20 to 25 mm cartilage box on top of the trachea, built from 4 cartilages: thyroid, cricoid, and 2 arytenoids that swivel like small doors. The folds run from the thyroid cartilage in front to the arytenoids behind. In a 4 kg cat each one is 10 to 15 mm long and 2 to 4 mm thick.

Each fold is a stack, not a string. A mucosal cover under 1 mm thick sits over a loose superficial layer that lets the cover slide, then a tougher ligament, then the thyroarytenoid muscle that forms the bulk. That loose middle layer lets the fold vibrate as a wave instead of swinging as a rigid bar. When scar tissue stiffens it, the wave breaks up and the voice turns rough at every pitch.

The opening between the folds, the glottis, is 4 to 6 mm wide at rest and opens to 8 to 10 mm on a deep breath. A cat breathing through a 3 mm gap is working 2 to 3 times harder than normal, and that number, not the sound of the meow, decides an emergency.

Two frequency classes: 25 Hz and 500 Hz

The purr is the low class. It runs at 20 to 30 Hz, usually 25 Hz, and continues on inhale and exhale for 10 to 30 minutes. Airflow alone cannot drive that rate in a 4 kg animal, so the timing comes from a brainstem oscillator firing the laryngeal muscles about 25 times a second.

The meow is the high class. A healthy adult calls at 300 to 900 Hz, with most meows between 400 and 700 Hz. Kittens start at 600 to 900 Hz near 8 weeks and settle into the adult range by 6 to 8 months as the folds grow from roughly 7 mm toward 15 mm. The 2 classes sit 15 to 30 fold apart, a gap the dog and the human voice do not have.

Why 1 mm of length moves the pitch

Frequency rises with the square root of tension and falls with length. Double the tension and pitch climbs 41 percent, not 100 percent. Add 10 percent to the vibrating length, about 1.3 mm on a 13 mm fold, and pitch drops roughly 9 percent, taking a 500 Hz meow to about 455 Hz.

Swelling that adds thickness but no length lowers the voice, which is why a 2 mm polyp drops the call by 30 to 80 Hz while the other fold stays normal. Two folds running at slightly different rates also add the buzzy edge owners call hoarse, which acoustic software reads as jitter above 1 percent.

Three hoarseness categories a vet sorts first

Category	Onset in days	Pitch shift	Exam finding	Book within
Swelling: laryngitis, herpesvirus, calicivirus	2 to 5	Down 30 to 80 Hz	Red folds with 1 to 2 mm of edema	72 hours
Nerve failure: laryngeal paralysis, thyroid mass	14 to 60	Down 50 to 150 Hz	1 arytenoid fixed, 3 to 5 mm gap	7 days
Mass: polyp, nodule, tumor	30 to 120	Unstable, 100 Hz swings	2 to 5 mm lesion on 1 fold	14 days
Age-related thinning, 10 years and up	180 to 720	Down 20 to 40 Hz	Thin folds, no mass, full motion	2 weeks, routine

Swelling is the most common of the 3 and the quickest to fix. A cat with herpesvirus or calicivirus sheds for 7 to 14 days and often loses the meow for 3 of them; the folds look red and puffy, and most cases settle without antibiotics because the cause is viral. A cat that is also sneezing, runs a fever, or stops eating for 24 hours needs a visit inside 72 hours instead of watchful waiting.

Nerve failure is the group that gets missed. Laryngeal paralysis leaves one or both arytenoids stuck near the midline, so the glottis cannot open past 3 to 5 mm and the cat breathes with a noise on inhale. Cats hide it for weeks, then show a raspy voice plus exercise intolerance after 2 to 3 minutes of play. Any cat over 8 years with a changed voice also needs a thyroid check, since an enlarged gland can press the recurrent laryngeal nerve.

A mass is the slowest group and the one where 14 days matters. Polyps, nodules, and carcinomas grow 1 to 2 mm a month and rarely hurt, so the only early sign is a voice that drifts for 4 to 8 weeks. Laryngoscopy finds lesions down to 2 mm; a plain radiograph misses anything under 5 mm.

The 10-minute workup

Most vets grade arytenoid motion 0 to 2, and that score plus fold length decides the next step. Laryngoscopy takes 2 to 3 minutes under light anesthesia. A blood panel adds a T4 for cats over 8 years.

Voice changes that are not disease

Hoarseness after 1 intubation clears in 24 to 72 hours. A kitten's voice cracks for 2 to 4 weeks around 4 to 6 months as the larynx lengthens. Cats over 10 years lose 20 to 40 Hz of range, which is normal aging. The pattern to watch is a hoarse month, not a day.

Red flags: 24 hours, 48 hours, 2 weeks

Go now if the cat is open-mouth breathing, has blue or grey gums, or has collapsed. Go within 24 hours if the meow has vanished or the cat drools and cannot swallow. Go within 48 hours if there is a new noise on inhale at rest. Book within 2 weeks for any voice change lasting 14 days or more with normal breathing.

Record 3 clips before the visit

Record 10 seconds of the meow, 3 times a day for 3 days, on the same phone at about 30 cm.
Film 30 seconds of breathing at rest from the side.
Keep a 7-day food and water log.

What to do this week

Time the hoarseness in days before you call, because 14 days is the line between watching and scoping.
Count resting breaths for 30 seconds; over 40 a minute means a same-day visit.
Check the gums: pink is normal, and blue, grey, or white means the airway or oxygen is failing.
Skip cough syrups; a 10 to 15 mm fold does not respond to them, and some human products are toxic to cats.

More on how cats read the world: color vision and white cell counts, plus the breed quiz for body size.

Terms mentioned in this article

MM T4

Frequently asked

How long are a cat's vocal folds, and does size affect pitch?

Each fold is about 10 to 15 mm long in a 4 kg cat, 2 to 4 mm thick, inside a larynx 20 to 25 mm tall. Pitch falls as the vibrating length grows, so a kitten with 7 mm folds calls at 600 to 900 Hz and an adult at 300 to 900 Hz, mostly 400 to 700 Hz, once the folds reach full length.

Why does my cat purr at 25 Hz but meow at 500 Hz?

The 2 sounds use different drivers. The purr runs at 20 to 30 Hz from a brainstem oscillator firing the laryngeal muscles about 25 times a second, on both inhale and exhale. The meow is airflow driven fold vibration at 300 to 900 Hz. That is a 15 to 30 fold gap between the registers.

How long can a hoarse cat wait before a vet visit?

Two weeks is the usual line for a voice change with normal breathing, because polyps and tumors drift slowly for 4 to 8 weeks. Move to 72 hours with fever or after 24 hours without food, 48 hours with a new noise on inhale, and 24 hours if the meow is gone or the cat cannot swallow.