How to Classify Your Hair With the FIA System

The Fia info was copied from this site.  The info in purple was added by me.

Fia's Hairtyping System

FIRST CLASSIFIER:

The straight ones 
1a - stick straight
1b - straight but with a slight body wave, just enough to add some volume, doesn't look wavy
1c - straight with body wave and one or two visible S-waves (e.g. nape of neck or temples)

The wavy ones
2a - loose, stretched out S-waves throughout the hair  Beachy waves, rock star waves
2b - shorter, more distinct S-waves (similar to waves from braiding damp hair) Princess Hair
2c - distinct S-waves and the odd spiral curl forming here and there A mix of waves and curls and some pieces that have a mix of S and C shapes.  On NC.com this is often referred to as "Wurly" hair.

3) The curly ones 
3a - big, loose spiral curls  Like a telephone cord.  (Anyone else old enough to know what that is?)
3b - bouncy ringlets  Ringlets the size of a pinky finger.
3c - tight corkscrews  Ringlets the size of a pencil or straw.

4) The really curly ones  Common among African Americans.
4a - tightly coiled S-curls 
4b - tightly coiled hair bending in sharp angles (Z-pattern)

SECOND CLASSIFIER
What (most of) your individual strands look like

F - Fine
Thin strands that sometimes are almost translucent when held up to the light. Shed strands can be hard to see even against a contrasting background. Similar to hair found on many people of Scandinavian descent.

You can also try rolling a strand between your thumb and index finger. Fine hair is difficult to feel or it feels like an ultra-fine strand of silk

M - Medium
Strands are neither fine nor coarse. Similar to hair found on many Caucasians.

You can also try rolling a strand between your thumb and index finger. Medium hair feels like a cotton thread. You can feel it, but it isn't stiff or rough. It is neither fine or coarse.

C - Coarse
Thick strands that where shed strands usually are easily identified against most backgrounds. Similar to hair found on many people of Asian or native American descent.

You can also try rolling a strand between your thumb and index finger. Coarse hair feels hard and wiry. As you roll it back and forth, you may actually hear it.


Science-y Hair Blog explains how you can measure your hair will a ruler to tell the texture.  See this link.

THIRD CLASSIFIER
Your overall volume of hair

Put your hair in a ponytail with as much hair as possible in it. Don't bother with the way it looks - the goal is to have most/all of your hair in there. If it means it sits smack dab on top of your head, put it there.

Measure the circumference of the ponytail. If you have bangs and/or you can't get all of your hair in there adjust according to how much of your hair you have measured.

To measure the circumference - take a piece of string, or a soft tape measure (the kind used by dressmakers). Wrap the string or tape measure <i>around</i> your ponytail - just below the elastic you have in to hold the ponytail together. Read the corresponding number from the tape measure, or hold the string at the length you've measured and use a ruler to determine how much it is. The number given is the circumference of your ponytail.

i - thin (less than 2 inches/5 centimeters)
ii - normal (between 2-4 inches or 5-10 centimeters)
iii - thick (more than 4 inches/10 centimeters)

NC.com link with photos of different curl patterns.

Your curl pattern may not fit neatly into only one category.  It is common to see a mix of curl patterns on one head.  This is especially true for wavies.  Some hair just doesn't fit any description.  
Figuring out your hair texture can be tricky as well.  Your hair stylist should  be able to tell you your hair's texture (Kinky or dry hair has been known to throw some stylists.  See below).  If you compare your hair with your friend's hair, this should help you with figuring out your hair's texture.  
Live Curly Live Free has a service where you send in your hair and they tell you your hair's texture, porosity, and elasticity.  The hair analysis I would recommend for a similar price is GoosefootPrints on ETSY.  At GoosefootPrints you get your hair analysis, pictures of your hair under a microscope, and a helpful document that helps you interpret your hair analysis results.  See my sample GoosefootPrints Analysis post. 
If your hair is dry and therefore has a rough feel, you may mistakenly think your hair is coarser then it actually is.  If your hair has some kinky pieces mixed in, this can also make you assess your hair as coarser then it actually is.  Any ethnicity may have kinky hair.  I'm as pale as they come and 40% of my hair has kinks (my GoosefootPrints hair analysis told me this).  This link explains the difference between kinky hair and curly hair with helpful illustrations.  Hair is kinky because of the way it twists (see illustration in link). Another type of kinky hair is where the hair shaft narrows and widens.  I have both of these types of kinks in my hair.