Freezing Degree Days Calculator
Calculate freezing degree days to measure cumulative cold exposure. Understand how prolonged cold affects soil, buildings, and energy use.
Temperature Inputs
Reference temperature (typically 0°C/32°F)
Actual average temperature for the day
Freezing Degree Days
Enter base temperature and average daily temperature to calculate freezing degree days
What Are Freezing Degree Days?
Freezing degree days measure how cold a period has been by adding up the difference between a base temperature and the actual daily temperatures. It's like keeping a running total of how much the weather has been below freezing.
Farmers use FDD to know when soil might freeze deep enough to damage crops. Builders track it to understand frost depth in the ground. Energy companies use it to predict heating demands. Even homeowners might want to know when pipes could freeze.
Unlike just looking at the temperature, FDD tells you about the cumulative effect of cold weather over time.
Freezing Degree Days Formula
Daily FDD Calculation Formula
Freezing Degree Days = Base Temperature − Average Daily Temperature
FDD is calculated only when the average daily temperature is below the base temperature:
- • Base Temperature: Usually 0°C (32°F) - the "freezing point"
- • Average Daily Temperature: The day's actual average temperature
- • Result: Positive number showing degree-days of freezing
Example: Base = 0°C, Average = -5°C
FDD = 0°C − (-5°C) = 5 degree-days
Freezing Degree Days Examples
Daily Temperature Calculations
| Base Temp (°C) | Avg Daily Temp (°C) | Daily FDD | Interpretation |
|---|---|---|---|
| 0 | -5 | 5 | Moderate freezing day |
| 0 | -2 | 2 | Light freezing |
| 0 | 3 | 0 | No freezing |
| 0 | -10 | 10 | Severe freezing day |
FDD accumulates over time. 100 FDD might mean 20 days at 5°C below freezing, or 10 days at 10°C below freezing.
Freezing Degree Days FAQs
What's the difference between FDD and heating degree days?
FDD measures cold below freezing, while heating degree days measure cold above freezing. They serve different purposes for energy and agriculture.
Why use 0°C as the base temperature?
0°C is the freezing point of water, which is important for soil freezing, pipe freezing, and many agricultural concerns.
How do farmers use FDD?
Farmers track FDD to predict frost depth, determine when to plant cold-hardy crops, and protect overwintering plants.