It’s hard to set i:c ratios if your basal insulin is not providing reliably in-target blood glucoses over the 24 hour period, and with NPH you don’t get that. That being said, you’ll have to do it trial and error. Keep a small notebook with times and test results at left, what you ate with grams in the middle, and what NPH and Novolog units you gave.
Use small numbers of carb grams and small numbers of Novolog first, figuring how far up a 4 gram tablet of glucose takes you. When you’re 160-180 mg/dL, you can inject one unit Novolog to see your sensitivity - how far down one unit will take you. You’ll have to do this for each third of the day since your NPH varies your baseline instead of being able to depend on always starting from a blood glucose of approximately 100 mg/dL.
You’ll also need to see how far up small numbers of starch, milk products, and fruit take you separately, since each affects your blood glucose differently. Note how fast each works - and with pizza, note you’ll need an immediate injection plus a later one in 3 hours.
If able to move from NPH to an 18-24 hour basal insulin, do so. The basal insulins sometimes require two shots a day due to spikes and length of action varies with individuals, but you can get a more stable round-the-clock baseline with them - then i:C ratios become more stable to figure, too.
Everyone uses a greater amount of insulin per carb in the a.m. than noon and supper, due to tamping down Dawn Phenomenon.
Newbies usually start with ratios 1unit:15gm and do trial and error from that, but with NPH as your basal, I can’t predict.
I’m on 1:3 in the morning; 1:4.5 noon and supper. I’m taking prednisone so that skews my regular i:C ratio mammothly! Good luck, best wishes, etc.