Insulin to carbohydrate (CHO) ratio

You may already be using an insulin to carbohydrate (CHO) ratio to calculate how much insulin to take at mealtimes. This is based on the number of units of insulin for each 10g of carbohydrate or CP (carbohydrate portion).

When using a pump it is more common to have a ratio where 1 unit of insulin is given for a calculated amount of carbohydrate. This allows a more accurate bolus dose calculation.

Your diabetes team may decide to continue your present insulin to carbohydrate ratio when you start pump therapy. If this is the case, and you know what your ratio is, then please move on to the next topic.

Otherwise, follow the steps below to calculate your pump insulin to carbohydrate (CHO) ratio (this calculation is also available in a printable worksheet here):

Calculate your total daily pump dose (TDD) as described in the previous ‘Initial insulin doses’ topic. Divide 400 by your TDD to work out how many grams of carbohydrate 1 unit of insulin will cover.

ALWAYS CHECK THESE CALCULATIONS WITH A HEALTHCARE PROFESSIONAL BEFORE PROGRAMMING YOUR PUMP

Calculate your total daily pump dose as described in the previous ‘Initial insulin doses’ topic.

Total daily pump dose = 30 units

Rounded down, this means you will need approx 1 unit of insulin for every 13 g of carbohydrates.

Insulin to Carbohydrate Ratio Ready Reckoner

If you’re a DAFNE graduate and are starting with an insulin pump, then you might be using carbohydrate portions (CPs) instead of grams. To use your insulin pump you will need to switch to counting grams. The insulin to carbohydrate ratio ready reckoner helps make this conversion clear.

Conversion from carb portion (CPs) to grams (g) of carbohydrate

Carb Ratios	Bolus Calculator
Insulin / CP	1 unit insulin to /grams of carbs
0.5:1	1 unit / 20 g
1:1	1 unit / 10 g
1.5:1	1 unit / 7 g
2:1	1 unit / 5 g
2.5:1	1 unit / 4 g
3:1	1 unit / 3 g

Boluses

You should give meal-time boluses ideally 5–15 minutes before meals. Your pump may have different speeds/ways of delivering the mealtime bolus.

You can use different bolus modes depending on the type of food being eaten. Your insulin pump team can discuss the options with you.