How can I shrink hand knitted wool blend hat to original size?
It doesn't matter whether the hat was made with knit or crochet.


Suppose it has wool fiber content, or unknown fiber content.  If unknown, we must assume it has some wool in it, to play it safe.

Premeasuring (in preparation for blocking).  Turn the hat inside out and lay it out flat on a table.  Measure the half-circumference of the hat by measuring the width of the cuff or bottom band.  Stand the tape measure on its edge to allow it to follow the natural curve of the hat, or allow your tape measure to come up from the horizontal plane if necessary to follow the curvature of the hat.  Also measure the height (from the edge, or folded cuff edge, to the top, or center of the crown). Write down the measurements.  Now turn the hat right-side out and put it on.  Pinch the cloth with your fingers and look in the mirror, to try to figure out how much too big the hat is for you, in each direction.  Keep the fact that you're working with a half circumference measurement in mind.  Subtract from what you measured and write down what you think the ideal measurements would be for this hat.

Washing.  Even if it's wool, you can wash the hat by hand in cold water.  Woolite would be a reasonable choice but laundry soap or detergent labeled for baby clothes would also work.  Don't scrub, just swish the garment around and let it soak for five minutes.  Rinse several times, using a tiny bit of fabric softener in the last rinse.  When you're done, do not wring (twist); instead, gently squeeze dry to the point where it's not dripping copiously.  Since your garment is small, if you like, you could put it in a colander and then push a similarly shaped bowl down on it to get a bit more water out.  (If you are a body builder, do not use much strength when pushing down on the colander.)  Now, lay out a clean, dry, old towel and put your garment on it.  Start to roll the towel by folding over the short end and continuing to roll it up, with the garment going along like a jelly roll.  When you've rolled up the whole towel, you may fold it in half.   Wait a few minutes and unroll. Lay the garment on another old towel to dry.  Or lay it flat on a "sweater dryer."

Blocking.  You will work with a steam iron with a misting button.  If the garment is fully dry when you start, you'll mist it with water (both front and back), but if it's still a little damp, you can skip the misting.  Lay it out on an ironing board or a folded towel on an old table.  Measure.  Let the damp fabric bunch up a bit if necessary to get the desired measurements that you wrote down before washing.  Preheat your iron to medium and switch on the steam feature.  Cover the garment with a "press cloth," a clean piece of cotton cloth or a clean, thin dish towel.  In a pinch you could use an old cotton T-shirt.  Use the iron like a hover board over the fabric sandwich.  The idea is to create steam which will encourage the garment to take the desired measurements.  Don't press down on the fabric sandwich, and don't let go of the iron.  You may allow the iron to come into the tiniest bit of contact with the top (cotton) layer.  From time to time, set the iron down and lift up the cover cloth, to check if the desired measurements have been achieved yet. 

When you've reached the desired dimensions, uncover the garment but don't move it, and allow it to air dry in place.

If there's no wool fiber content, the garment will probably not benefit from blocking.  In that case, follow Method 2.
Suppose there is no wool in this hat.  Hand wash as described above (except you may squeeze a little harder).  After the towel roll-up step, put your garment in the dryer along with a clean, dry old towel.  Set the dryer on "gentle," "delicate" or "low."  Check, and give it a few more minutes if necessary.  The dryer will activate the elasticity in the fibers.  If the garment is cotton or mostly cotton, there may not be any elasticity to activate.  In this case, repost with a photograph of the hat and information about the dimensions.  It might be possible to give the hat a little bit of reconstruction.