This video shows how to do the long tail cast on. First is a very quick refresher for those who already know how to do it, followed by an in-depth discussion of how to do the long tail cast on effectively.
In Brief
Leave a tail as long as you need. Make a slip knot. Put your finger and thumb in between the two strands making sure that your thumb holds the tail stand. Grasp both strands of yarn with the rest of your fingers. With the right needle go into the loop on the thumb and pick up the strand on the index finger. Continue to do that for all the stitches you need to cast on.
So, that is a very brief overview. Now, I will go over it in detail.
Details
This cast on is also known as continental, double, two-tailed, knit half-hitch, German, slingshot, finger, Y, two strand, one needle, single needle.
Advantages
The long tail cast on is probably the most commonly used cast on, at least among Western knitters. This is because it is:
- very versatile, you can use it for almost any project
- stretchy
- stable
- fairly easy to do, once you know how
- fairly quick to do
- edge is neat and attractive
Disadvantages (these are easily resolved and are discussed below)
Some people don’t like it because they find that it is:
- hard to estimate the length of yarn to leave for your long tail
- it is not stretchy enough
Estimating length
As the name implies, you need to leave a long tail, plus a tail that you will weave in at the end.
You need to estimate the amount of yarn that you leave before making your slip knot. If you don’t have enough, you will run out of yarn before you finish the cast on. If you have too much, you will waste yarn and either have to cut off the excess or you will have to deal with an unnecessarily long tail that may get in the way.
There are several approaches to estimating this length of yarn:
- Just pull out an amount of yarn you think will suffice and start. This is very haphazard and inaccurate unless you know beforehand approximately how much yarn you need, for example, if you regularly make socks with fingering weight yarn and you know that one arm’s length of yarn is about what you need.
- Make your tail 3 times as long as the cast on edge is wide plus the weaving in tail. You can look at the schematic or calculate how wide it should be by dividing the gauge per inch (or 2.5 cm) by the number of stitches cast on. If the gauge is 20 sts per 4 inches (10 cm) that translates to 5 sts per inch (or 2.5 cm). If you need to cast on 50 stitches, divide 50 by 5 and you are aiming for a width of 10 inches (25 cm). Your tail should be 10 inches (25 cm) X 3, or 30 inches (75 cm) plus a tail for weaving in. The amount of yarn you use will vary depending on the weight of your yarn and how tightly you cast on. You can try this and see if it works for you.
- Use a chart that gives you estimates for the amount of yarn per stitch needed depending on yarn weight. Leave a tail to weave in and then add the length per stitch multiplied by the number of stitches you need to cast on. Again, your results might not be the same as whoever has prepared the charts, so you may need to adjust. One such chart can be found here.
- Cast on a small number of stitches (eg. 10), count them, rip out the cast on and measure how much of a tail that used, divide by the number of stitches and then multiply that by the number of stitches you need to cast on.
- Wrap the yarn around the needle as many times as you have stitches. If you have more then, let’s say 20 stitches, wrap the yarn around the needle 10 times and then multiply that length by the number of groups of two stitches.
- Use two ends of the same ball or ends from two balls to do the cast on. This leaves you with two extra ends of yarn to weave in. It is not always easy or convenient to do this.
Understanding the formation
It is important to note that the yarn that is over the thumb and wraps around each stitch underneath the needle uses less yarn than the strand of yarn on the index finger and wraps around the needle. This may not be the case when using really tiny needles, but for me, it is true even on 2 mm (US #0) needles.
Where length is estimated in the above methods, it is assumed that you will hold the tail of the yarn over your thumb (whether you are using the continental method (slingshot) or English style) when casting on. The yarn that goes over your index finger is used at a faster rate than the yarn that is over the thumb unless you are casting on using both knits and purls.
The yarn thickness, not the needle size determines how much of a tail you need. Regardless of needle size, the amount of yarn that is used to create the wraps underneath the needle remains relatively consistent. The amount of yarn that is used for the stitches sitting on the needle changes much more dramatically with changes in needle size.
In the photo to the right, I have cast on 11 stitches onto e
Then, I pulled the stitches off the needle, leaving the slip knot in place. I pinned the slip knot down and pulled the rest of the stitches apart. 
Slip knot or not
You can start with a slip knot or you can just twist the yarn on to the needle to begin. Some people do not like the slip knit in their knitting, just like they do not like other knots in their knitting. I personally find that starting with a slip knot gives a slightly cleaner beginning corner. That said, I don’t always start with a slip knot. Try both methods on your gauge swatches and see which you prefer after several rows of knitting.
With a slip knot
Make a slip knot, place the needle into the slip knot and hold this in your right hand. Pinch together the thumb and index finger on the left hand. Slide these between the strands coming from the slipknot, making sure that the tail end is over the thumb and the ball end is over the index finger. Close the other three fingers over the two loose strands going to the tail and the ball.
Without a slip knot
With your right hand, pick up the yarn at the point you want to start. Have the tail end toward you. Pinch together the thumb and index finger on the left hand. Slide these between the strands coming from your right hand, making sure that the tail end is over the thumb and the ball end is over the index finger. Close the other three fingers over the two loose strands going to the tail and the ball. If you turn your palm towards your face, you will see a triangle with the base (horizontal side) at the top.
Bring the needle through the centre of the triangle you have made, from right to left, moving away from you. Pull the needle up and toward yourself so that it is standing vertically pulling the yarn towards you like a slingshot. Secure the strand on the needle with your right index finger. Rotate the needle clockwise around the two strands going to your index finger and thumb. Turn your left hand back so that the thumb is pointing up and to the right.
Creating the cast on stitches
Move your right thumb and index finger to just in front of the previous stitch. Bring the needle towards you and down. With the tip of the needle go up through the loop on your thumb. Scoop up the strand of yarn going from the index finger to the needle by going over it and scooping towards yourself and back down through the loop on your thumb. Ensure that the new stitch is on the shaft of the needle not just on the point. Snug the new stitch up to the tips of your thumb and index finger. This usually leaves an appropriate amount of space between the stitches. (Drop the loop off your thumb, move your thumb underneath the needle to draw the loose yarn up and towards yourself to snug the stitch and to prepare for the next stitch.
You may need to reposition your fingers occasionally, possibly after every stitch if you are just learning.
Repeat these movements for all the stitches you need to cast on.
Comparing the long tail to other cast-ons and knitting
When you do the long tail cast on, you are essentially knitting a row of stitches. Instead of knitting off an already formed row on the left needle, you are knitting stitches as you form them off your left thumb. Your thumb essentially becomes your left needle.
This cast on combines the backwards loop cast on and the first row of knitting into one motion. Doing it this way, you create a much more sturdy cast on than if you did a backwards loop and simply knit or purled into it because the loops on a backward loop cast on are as large as the needle you are casting on with, the loops in the long tail cast on are only as large as the diameter of the yarn you are using plus some ease. If you were to do a backwards loop cast on with a needle that is about the same size as your yarn and then purl the first row, you would have a cast on that is identical to the long tail cast on.
The advantage of the long tail cast on is that it is easier and faster to work and you only need the size of needle you are using for the project.
The cast on can count as your first row
Because of the fact that the long tail cast on is really a variation of a backwards loop cast on with the first row already worked, it often counts as both the cast on and the first (right side) row. However, when this is not practical for the project at hand and the cast is not counted as the first row. In my own upcoming top-secret blanket pattern, I do not specify a cast-on, but if the long tail cast on is used, it does not count as the first row or it would disrupt the way that the pattern goes together.
Ensuring an elastic cast-on
How the stitches sit on the needle will determine how stretchy this cast on is. For a long time, I wondered why everyone thought that the long tail cast on was so stretchy because I did not find it so.
What doesn’t make the cast-on elastic
Some people suggest casting on with two needles to make the cast on more elastic. However, that only makes the first row of stitching loose and unattractive and does little for added flexibility. As we saw in the previous section, only the thumb yarn is actually part of the cast on. The index finger yarn is, in fact, part of the first row of knitting. I cannot imagine anyone suggesting to do some cast-on and then knit the first row of the project with two needles. It just would not help. Suggesting that you cast on with two needles is suggesting exactly that.
What causes the tightness then? Tightening your stitches too much and casting on your stitches too closely together. So you can be doing the cast-on correctly, doing all the correct movements, but if you bunch your stitches together or tighten the thumb loop too tightly you will have a firm, non-stretchy cast on instead of a lovely elastic one.
What does make the cast on elastic
Again, as we saw in the section above, the actual cast on is made with the yarn on the thumb. If you tighten that too much or squeeze the cast on stitches together, leaving very little room for the yarn to travel from one stitch to the next, you will have a very tight cast on. There are two things you need to watch for:
- Snug each stitch to the needle but do not tighten with a death grip. Form your stitches on the shaft of the needle, to make them the same size as your stitches on other rows and to make them easy to get into on the next row.
- Ensure that you have a comfortable distance between the stitches as you cast them on.
In the photos below, I have done swatches in the same yarn, on the same needles. In the first swatch, I cast on very tightly, both pulling the yarn on the needle tightly and leaving no room between the stitches (top left). On the other swatch, I cast on, snugging the yarn to the needles and leaving a space between the stitches as described above (spacing the stitches by placing my thumb and index fingers in between stitches).
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The resulting swatches are shown below with the highly cast on swatch underneath the swatch that was cast on in a relaxed manner. The swatches are unstretched in the first photo and stretched as far they could stretch comfortably in the second photo. As you can see, how tightly you cast on and how closely you place the stitches makes a significant difference. Both swatches have the same number of stitches and both have the same number of rows. Both are done with the same ball of yarn and with the exact same needles. The one that was tightly cast on pulls in, even when not stretched. It does not stretch out as far as the relaxed cast on.
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In the last swatch, I did a relaxed long tail cast on over two needles. The swatch is the same width as the relaxed cast on over one needle, however, if you look at that cast on and first row, it looks messy and that first row is very loose. This is just as we would expect given what we know about how the cast on works.
Perhaps surprisingly, the cast on does stretch a bit more when the piece of knitting is stretched as far as it will comfortably stretch.