Calculating your heating degree days is straightforward once you know the Degree Days formula and what each input means. This guide explains the method in plain language, walks through a manual calculation, and gives worked examples you can follow — then you can do it instantly with the Degree Days Calculator.
What is Degree Days?
The Degree Days calculation tells you your heating degree days from a few simple inputs. The figure you are solving for here is the heating degree days.
The Degree Days formula
This calculation combines several inputs through a multi-step method rather than a single one-line formula. Enter the values below and the calculator resolves each step in order. The inputs it needs are:
- Base temperature — a value measured in °C. Example: 18 °C.
- Average daily temperature — a value measured in °C. Example: 10 °C.
How to calculate it step by step
- Write down the base temperature (for example, 18 °C).
- Write down the average daily temperature (for example, 10 °C).
- Apply the formula above to get your heating degree days.
- Double-check the result with the Degree Days Calculator.
Worked examples
Example 1
| Input / Output | Value |
|---|---|
| Base temperature | 18 °C |
| Average daily temperature | 10 °C |
| Heating degree days | 8.0 |
| Cooling degree days | 0.0 |
With base temperature of 18 °C and average daily temperature of 10 °C, the heating degree days works out to 8.0.
Example 2
With base temperature of 36 °C and average daily temperature of 10 °C, the heating degree days works out to 26.0.
| Result | Value |
|---|---|
| Heating degree days | 26.0 |
| Cooling degree days | 0.0 |
Example 3
With base temperature of 9 °C and average daily temperature of 10 °C, the heating degree days works out to 0.0.
| Result | Value |
|---|---|
| Heating degree days | 0.0 |
| Cooling degree days | 1.0 |
Tips for an accurate result
- Keep your units consistent — mixing, say, months with years or grams with kilograms is the most common source of error.
- Round only at the very end. Rounding inputs early can shift the final answer noticeably.
- Re-run the numbers whenever an input changes, rather than estimating from an old result.
Prefer not to do the maths by hand? — the Degree Days Calculator does it instantly, for free, with the formula and a worked example built in.
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