CSM Foot Calculator

I created a calculator to help figure out how many rounds to knit for the foot after finishing the heel and before starting the toe for a CSM sock.

For the best results, knit a sample tube (you can later rip it out and reuse the yarn). This tube should be knit with the desired yarn at the tension you have determined is best for it, with the cylinder on which you are making the sock, and you have created a fabric you think will fit the foot circumference you want. Use a washed sample or at least let it relax off the machine for a while before counting rounds (rows) .

Measure the foot or look up what the foot length is by shoe size. (I use this chart.) Count the number of rounds (rows) you get in 3 inches and divide that by 3 for the average rounds per inch (RPI).

Input your numbers into the fields below where there is an asterisk. There is instructions included with the fields you need to input.

This calculator works for me, I make no guarantees, I just offer it as a tool. Remember, socks don’t have to be exact; knitting stretches a bit when it needs to and it will fit a range of sizes, so you just need a number to get you in the ballpark for the desired foot size.

I do not charge to use the calculate, but if you find this useful and come back frequently to use it and would like to help me offset the cost keeping the website and calculator online, donation in any amount is welcome.  Click the donate button for a  Paypal page.

This calculator is free to use, but if you find this useful and come back frequently to use it and would like to help me offset the cost of keeping the website and calculator online, an occasional donation in any amount is welcome.  Click the donate button for a  Paypal page.

21 Replies to “CSM Foot Calculator”

  1. Thank you so much! I spent several hours tonight trying to develop this formula and finally put it aside to try to sleep on it. I am so relieved that you have already done that work for me.

  2. Sooooooo I didn’t swatch with Lycra. Wrong move since I used it for my sock. Love this though. Thank you!

    1. I don’t use Lycra, So I can’t really say how you might adjust for using it. You might have to plan for a smudge of positive ease when using Lycra.

  3. Thank you so much for this wonderful calculator. I wish the negative ease was by inches. The percentage is too confusing for my brain….. not really sure how it works

    1. Sorry Dorinda for the late reply. Usually socks will have some negative ease, just try .95 or .90 if 1 is giving you too long of a sock or you find that your sock doesn’t shrink a bit in the wash. The results at the bottom show the knitted foot length in inches after you use .95 or .90 for 5% or 10% negative ease. You can subtract the results from the foot length in inches that you input to see how much shorter in inches adding negative ease will cause. Use a calculator if you need to. If you are knitting for a wide foot, try 1.05 or 1.10 for the negative ease field. A 5% or 10% longer sock will allow it to stretch wider around.

    1. Hi, Dorinda. An example is my foot length of 10″. A 10% negative ease would be to knit the sock to a total of 9″ which is 10% less than 10″. If I get 9 RPI, and if I subtract 3″ total to account for the heel and toe, 3″ x 9 RPI = 7″ for the foot. 7″ x 9 RPI = 63 rows for the foot between the end of the heel and start of toe. This math works easily, and is true for my own socks for which I knit 62 foot rows.

  4. Anyone else have an issue with losing inches in the toe and heel after engaging the heel spring? I kept wondering why my socks were shorter than I calculated. I’m going to change my ease to 1.05 to accommodate the increase in RPI when I engage the heel spring and see if that helps. Or I could do the math and measure the difference in RPI but yuck. 😏

    1. Sorry for the delayed reply. I didn’t get notified of the comment and just saw it. I use the heel spring for the entire sock so that probably why I don’t have and change in rpi for the heels and toes and my sock is the same size stitches throughout. Adding a smidge more ease should help. The other thisng you could do is turn the tension down a click or two to make the stitches a little bigger when you make a heel and toe. The problem with that is remembering to change it back when you remove the heel spring.

      1. You’re right about that. I’ve forgotten to do change the tension back too many times. I think I’ll go back to using my heel spring throughout to make it easier. Thanks for your response.

        1. Yes, there is a PayPal link right above the calculator. If you’d rather Venmo, or cash app, I could do that as well just message me through Facebook since you know who I am there and I will give you my links.

  5. Hi, there is something I don,t understand. When the rows in heel and toe are increasing normaly the number of food rows must decrease. It,S just doing the opposite? I,m lost

    1. When you’re doing the increases, after you have decreased you’re making the other side so it doesn’t really add or subtract from the number of rows.

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