When to use this calculator
Subtract entered effective rainfall from a chosen irrigation-depth target. Use effective infiltrated rainfall, not necessarily total gauge rainfall.
Explore the irrigation & applied water calculators for other questions in this topic. For a related calculation, use the Sprinkler Precipitation Rate Calculator: Convert sprinkler flow and coverage area into an average application rate.
PUTTING IT INTO PRACTICE
Rainfall Irrigation Offset: a worked example
The values below are an illustrative example, not a recommendation. Replace them with measurements or assumptions that match your question.
| Input | Example value |
|---|---|
| Selected net water target (mm) | 20 |
| Measured effective rainfall (mm) | 8 |
| Result | 12 mm |
- Check the input labels and enter the example values above.
- Apply the relationship: Remaining depth = max(0,target−effective rainfall).
- The result is 12 mm, rounded for display.
How to interpret your result
Use effective infiltrated rainfall, not necessarily total gauge rainfall.
A water-budget conversion does not establish the crop’s requirement. Use measured flow and effective rainfall where possible. Distribution losses and runoff can make gross application differ from water retained in the root zone.
Frequently asked questions
Does one millimetre of rain equal one litre?
It equals one litre over each square metre of collection area. Total volume therefore depends on both depth and area.
When is the rainfall irrigation offset calculator useful?
Subtract entered effective rainfall from a chosen irrigation-depth target. Use effective infiltrated rainfall, not necessarily total gauge rainfall.
How do I use the rainfall irrigation offset calculator?
Enter selected net water target (mm), measured effective rainfall (mm). The result updates automatically. Use the units shown beside each input; the example values illustrate the method.
Which formula does this calculator use?
Remaining depth = max(0,target−effective rainfall).
What should I check before using the result?
Use effective infiltrated rainfall, not necessarily total gauge rainfall.
How are results rounded?
Scalar numbers display up to six decimal places, with scientific notation for very large or small values. Text, fraction, date and schedule outputs use the format described on the tool. Intermediate calculations use JavaScript floating-point arithmetic. Keep sensible precision for your measurements.
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