August Reboot Series - A Question for an Expert

This month I'm going to be doing some re-posting of older blog posts. Some like this one will have updates included as when I reread I often realize I've learned something new since the original post went up.  I hope to have all new interviews every Friday but many Pros take the month of August off and in past years I haven't always been able to get enough interviews back to fill all the August dates.  (As predicted I sent out a much higher number than usual of interview invitations but I don't yet have a new one to post.) 

The title of this post was in the subject line of an email to me. 

The note reads:

Hi Robin,

After about 70 years of knitting, I didn't realize I wouldn't know the answer to this question until I came upon it. If a pattern calls for size 4 mm needles and farther on asks you to use needles one size larger, are they asking you to use size 4.5 mm or size 5 mm?

 

My answer:

You need to look at the pattern source. Even then you may not match your needle with the designers plan. U.S. needles are all sized as whole numbers except for the 1 1/2, 2 1/2 and 10 1/2. (Of course this depends on what chart you look at and has changed since I wrote the original post.) If the pattern was written with U.S. sizes and converted to metric, one size up is 4.5. However not all the charts agree on an exact equivalent for each size. 

 

Currently, metric sized needles are being quoted more often for accuracy, so the designer could mean one size up on the metric chart. The same problems exist with the old UK/Canadian system. I still have many of those needles as they belonged to my Mother and Grandmothers. Japanese needles have another sizing system which doesn't align with any of these systems. The simple answer is that only the original designer or sample maker knows for sure what their one size up means if it is not listed specifically in the instructions or materials section of the pattern. I sell a lot of my patterns in the U.S. so I include both sizes in my patterns. Manufacturing of needles is done in many countries so they may work to more than one standard of sizing. 

 

How do you know for sure which is the best size....you already know what I'm going to say, by knitting a swatch.