Humans have 33 vertebrae in total, divided across five regions of the spine. That number comes with a caveat: by adulthood, several of those vertebrae fuse together, leaving you with 26 distinct bony segments. Whether someone counts 33 or 26 depends on whether they’re counting the individual vertebrae you’re born with or the separate bones in a fully mature spine.
The Five Regions of the Spine
Your spine is organized into five sections, each with a different number of vertebrae and a distinct job.
- Cervical (neck): 7 vertebrae, labeled C1 through C7. These allow you to turn, tilt, and nod your head. The cervical spine curves gently inward.
- Thoracic (middle back): 12 vertebrae, labeled T1 through T12. Your ribs attach here, forming the protective cage around your heart and lungs. This section curves slightly outward.
- Lumbar (lower back): 5 vertebrae, labeled L1 through L5. These are the largest and strongest vertebrae because they bear most of your body weight.
- Sacral: 5 vertebrae that fuse into a single triangular bone called the sacrum.
- Coccygeal: 4 vertebrae (sometimes 3, sometimes 5) that fuse into the coccyx, or tailbone.
The top 24 vertebrae, from the cervical through the lumbar region, remain separate and movable throughout your life. The bottom 9 fuse into two solid bones.
Why the Count Changes With Age
At birth, the sacral and coccygeal vertebrae are still individual segments. Over the course of childhood and early adulthood, they gradually ossify and merge. This process follows a predictable timeline, finishing around age 30. Once complete, the five sacral vertebrae have become one sacrum and the coccygeal vertebrae have become one tailbone. That’s why anatomy textbooks sometimes say 33 vertebrae and sometimes say 26 functional bones.
Not Everyone Has Exactly 33
The “33 vertebrae” figure is a standard teaching number, but spinal anatomy varies more than most people realize. The most common variation happens at the border between the lumbar spine and the sacrum. About 15% of people have what’s called a lumbosacral transitional vertebra, where the lowest lumbar vertebra partially fuses to the sacrum (sacralization) or the top sacral segment stays partially separate (lumbarization). In practical terms, this means some people effectively have 4 lumbar vertebrae and 6 sacral, or 6 lumbar and 4 sacral.
The coccyx also varies. Most people have 4 coccygeal vertebrae, but anywhere from 3 to 5 is normal. These variations are usually discovered incidentally on imaging and rarely cause problems on their own, though lumbosacral transitional vertebrae show up more frequently in people with low back pain and disc problems.
What Sits Between the Vertebrae
Between each pair of movable vertebrae sits an intervertebral disc, a pad of tough cartilage with a gel-like center that acts as a shock absorber. There are 23 discs in total: 6 in the cervical region, 12 in the thoracic region, and 5 in the lumbar region. There’s no disc between the first and second cervical vertebrae (C1 and C2), which is why that joint allows so much rotational movement, like shaking your head “no.”
Each disc is anchored to the vertebrae above and below by thin cartilage plates, roughly 0.6 to 1 millimeter thick. The discs in your lumbar spine are the thickest because they handle the most compressive force. When people talk about a “slipped disc” or “herniated disc,” they’re referring to the gel-like center of one of these 23 discs pushing through its outer wall.
How the Spine’s Shape Supports You
Viewed from the side, the spine isn’t a straight column. It forms an S-shaped curve, with the cervical and lumbar regions curving inward and the thoracic region curving outward. These alternating curves distribute mechanical stress, absorb impact from walking and running, and keep your center of gravity balanced over your pelvis. The 7-12-5 arrangement of movable vertebrae reflects the different demands on each region: the neck needs the most flexibility, the mid-back needs stability to protect organs, and the lower back needs strength to support the upper body’s weight.