Lots of people absolutely loathe the idea of knitting a tension piece in order to measure their knitting gauge. It seems such a waste of yarn and what if they run out and the only yarn left is in the tension piece. However it's most important that you do knit a tension piece before starting to knit the item. Everyone handles yarn and needles in a different way and this means that your tension may not necessarily match that of the designer even though you're using exactly the same yarn as was used in the pattern. It becomes even more crucially important to knit a tension square if you plan to substitute a different yarn from the one recommended in the pattern. Knitting a gauge sample allows you to judge whether the yarn you plan to use will suit the item in question or whether you may need to adjust the needle size to produce a more suitable fabric. It also allows you to measure the number of stitches and rows per inch before you start knitting the item you plan, which means that at least you will know that it will come out the size you expect. If you don't knit a tension sample, the chances are quite high that the item you plan to knit will not be the size you expect.

Lots of people knit their tension samples by casting on around 20-30 stitches, knitting 20-30 rows in stocking stitch or whatever the garment's main pattern is, and then casting off. This results in a curled up piece of knitting which is frankly a pain to measure particularly if the yarn is one which will not be blocked or pressed.

It's much better to knit your gauge sample with a garter stitch border, and then if necessary to block your sample before measuring it. The garter stitch border will stabilise the sample and make it much easier to measure the number of stitches and rows per inch. Try this way of knitting your tension piece:-

1. Cast on 30 stitches using the yarn and needles you bought in order to learn to knit, or if you are knitting a sample piece for a knitted item, using the needles for the main body of the knitted piece and the yarn you plan to use.
2. Work 8 rows in Garter Stitch (every row knit).
3. Next Row:Knit
4. Next Row:Knit 4 stitches, Purl to last 4 stitches, Knit 4 stitches
5. Repeat the last two rows until you have worked 30 rows of stocking stitch with a garter stitch edge.
6. Work 8 rows in Garter Stitch
7. Cast off

You now have a neat, reasonably sized oblong piece of knitting which is lying reasonably flat. Obviously this method of knitting a tension square won't work for every knitting pattern especially if it's lace which will be stretched, but it's a good way which works for many patterns.

Look at the paper ball band to see whether the yarn you are using can be ironed and if it says it can be ironed with the iron set to 2 dots or more, set up your ironing board. Lay the piece of knitting on the ironing board and place pins at intervals to hold it in shape. Set your iron to steam and the temperature required for the yarn, and hold it above the knitting for a few seconds till the steam penetrates the knitting. Do not touch the knitting as you may risk crushing and spoiling any raised texture stitches. Leave the knitting to dry then remove the pins. Be sure to use dressmaker's stainless steel pins, preferably the glass headed ones which are easy to see.

Next, you will need a ruler. Don't use a tape measure, these can stretch and then you will get an inaccurate measurement. Tension gauges in patterns are usually given over 4 inches or 10 cm but these two measurements are not quite the same - 4 inches is a little bigger than 10 cm as an inch is 2.54 cm. Most of the time this difference will not be too important as knitting is a very flexible fabric but it's an important difference to be aware of. If you work in inches you should do so throughout, and if you work in cm you should also use cm throughout your pattern.

Take your ruler and lay it on the tension sample, use your knitting needle to count the number of stitches across 10 cm/4 inches and the number of rows across 10 cm/4 inches. Write these numbers down somewhere where you won't lose the information - that is your tension gauge. If you're trying to match it to a pattern and your gauge matches the pattern at this stage, great you can go ahead. If not, you know at this stage that it's time to try different sizes of needles till you have matched the gauge of the pattern. It's far better to find that your gauge doesn't match that of the pattern at this stage, than later on when you've finished the garment.