Strap

Calculator

Star Flap Crochet Purse Pattern
Water Bottle Holder Crochet Pattern

Use this Strap Calculator to see how many starting chains you need for for the strap of either my Star Flap Purse pattern or my Water Bottle Holder pattern. The instructions below are the same for both patterns. 

Step 1: Create your strap Gauge swatch

Ch 39 and follow the Strap Instructions for Row 1 & 2 to create your strap gauge swatch. 

Step 2: Measure the Length of Your Gauge Swatch

After your strap gauge swatch is complete. Measure the length of it. You will enter this number in the first box of the calculator below. 

Step 3: Determine Your Desired Strap Length

Determine how long you want the strap to be. You will enter your desired length in the second box of the calculator below. 

Kid-Size Strap for Shoulder Bag: 33′′ (measured before it’s attached). This size makes the purse land at the hip of a child who is 4′ tall when wearing on a shoulder (not cross-body).

Adult-Size Strap for Shoulder Bag: 44″ (measured before it’s attached). This size makes the purse land at the hip of a woman who is 5.8′ tall when wearing on a shoulder (not cross-body). 

Adult-Size Strap for Cross-Body Bag:  55″ (measured before it’s attached). This size makes the purse land at the hip of a woman who is 5.8′ tall when wearing it cross-body.

Have another length in mind? You can enter any length into the calculator below. 

Kid-Size Strap: 33′′. This size makes the bottle holder (when water bottle is empty) land at the hip of a child who is 4’ tall when wearing the holder cross-body.

Adult-Size Strap: 44”. This size makes the bottle holder (when water bottle is empty) land at the hip of an adult who is 5.8’ tall when wearing the holder cross-body.

Have another length in mind? You can enter any length into the calculator below. 

Strap Calculator

This is how many starting chains you need to make the strap your desired length, based on the length of your swatch. 

This is the exact calculation you need (you don’t need to worry about multiples of 2 + 1 as the calculator rounds up to an odd number) 

Just In Case...

If the calculator told you how many starting chains are required, you are good to go and you don’t need to read this.

If for any reason the calculator isn’t working or you are interested in knowing the math behind these calculations, here they are: 

How to Check and Calculate Strap Starting Chains:

  • Ch 39 and follow Strap Instructions for Row 1 & 2.

  • Measure the length of your strap in inches (I will call this length A). If 10” then no calculations are necessary. Note that the 1st ch is just used once so when doing calculations, we will use 38 + 1.

  • Divide 10 by A = B. Multiply B by 38 = C.

  • Find the total length you want for the strap (example sizes are provided in the pattern). I will call this length D.

  • Divide D by 10 = E. Multiply E by C = F + 1 = G (round up if a decimal).

  • The total number of starting chains must be an odd number. Round up if necessary.

    Here’s an example: Let’s say that your 39 chains and 17 stars created a strap that’s 8” and you want a strap that’s 44”…

    Divide 10 by 8 = 1.25. Multiply 1.25 by 38 = 47.5. Divide 44 by 10 = 4.4. Multiply 4.4 by 47.5 =
    209 + 1 = 210. Round up to get an odd number = 211. Meaning you will need 211 starting chains to get a strap that’s 44”.