The answer to the question of course, depends on how long wide and thick you are!
I’m just under 6 feet tall and 185 pounds. My feet or my head end up off the end of a standard yoga mat and my knees and ankles press painfully through to the studio floor. A towel under your joints is one answer but the better solution is to buy a bigger, thicker, more comfortable yoga mat.
Standard discount yoga mats are about 1/8th of an inch thick and are usually too thin for comfort. Some stuffed cotton yoga mats are so thick they will even double up as occasional beds but, leaving health and eco concerns aside the most important thickness issue is balance. Many yoga postures call for a solid footing and good balance. If your yoga mat is too soft balance becomes much more difficult.
Most premium yoga mats are at least 1/4 of an inch thick but many also provide extra firmness to make up for this. If you like the grip and the construction of your standard yoga mat but, your weight pushes you through, or you suffer with arthritis, joint pain or simply sensitive ankles, elbows and knees, then you will really appreciate the much more comfortable 1/4 inch yoga mats.
The type of yoga you practice does have an impact on the type of yoga mat you buy. With more active styles being more suited to thicker yoga mats.
Length and width
My guess is that the standard 2 feet wide by 6 feet long yoga mat was designed for petite women and limited studio space. Don’t be restricted by this. Yoga mats come in all sorts of shapes and sizes. Up to 7 feet long and 3 feet wide is not at all unusual and, it’s possible to buy 6 feet square, or even round yoga mats (though I think my studio would charge me for the extra space!). If you can’t find a yoga mat you like you can even have one custom made.
A longer yoga mat is great for taller people and you can buy shorter yoga mats for children. Wider yoga mats are good for keeping more of your body off the floor and in cramped classes can gain you that little bit of extra arm room.
Don’t be tempted to buy a general exercise mat for yoga. I’ve tried them and they don’t work. The combination of grip, comfort and firmness needed in yoga is almost unique, and yoga mats are designed with this in mind.
A better yoga mat may only cost you $15 but it may make all the difference to your yoga practice. Talk to other yogis and yoginis, check out other peoples yoga mats and search the internet to find the perfect yoga mat for you.
Avoid cheap PVC mats the chemicals used in manufacture can damage your health.