| The only way to find the exact number is to do fasting tests where with no bolus insulin is active and there is no effect from eating. During a fasting test, ideally the blood sugar should remain nearly stable.
But I warn you about thinking that it is an exact number or a fixed number. Diabetics will see their basal insulin requirements have variations and changes over time, so fasting tests still need to be periodically done even after someone has successfully titrated the basal insulin for the first time.
There are calculators to make suggestions for starting doses. Their purpose is to provide a starting point which can then be refined with the procedures of basal testing. But they can only provide starting points because the calculation is generalized and doesn't calculate for individual variations caused by metabolic differences and individual levels of insulin resistance and how much native insulin production the diabetic has retained.
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MDI, Lantus and Novolog
A1c 10/09 -- 5.8%
A1c 4/09 -- 5.7%
A1c 10/08 -- 5.4%
A1c 4/08 -- 5.7%
A1c 8/07 -- 5.6%
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