Rainfall Accumulation Calculator
Turning a String of Daily Readings Into One Total
A single day's rainfall reading rarely tells the full story — what matters for irrigation planning, flood risk, or a rain gauge log is the accumulated total across a storm system, a week, or a growing season. This calculator takes any list of individual readings and returns both the running total and the average per period, sparing you the manual addition.
The Formula
Total Accumulation = Sum of all readings
Average = Total ÷ Number of periods
Average = Total ÷ Number of periods
Worked Example
| Day 1 | Day 2 | Day 3 | Day 4 | Day 5 | Day 6 | Total | Average |
|---|---|---|---|---|---|---|---|
| 0.5" | 1.2" | 0" | 0.3" | 2.1" | 0.8" | 4.9" | 0.82" |
Where This Matters
- Tracking a storm system — adding up hourly or daily readings during a multi-day storm gives the total accumulation figure that flood warnings and river forecasts are based on.
- Irrigation scheduling — farmers and landscapers compare weekly rainfall totals against crop water requirements to decide whether supplemental irrigation is needed.
- Climate record keeping — backyard weather station operators and citizen-science rainfall networks log daily readings and need running totals for monthly or seasonal reports.
How to Use This Calculator
- Enter the Daily Readings as a comma-separated list (for example: 0.5, 1.2, 0, 0.3).
- Select the Unit: Inches or Millimeters.
- Select Calculate to see the total accumulation and the average per period.
Related Calculations
Check whether heavy rain could contribute to coastal flooding with the Storm Surge Calculator, or see how snowfall might affect the day ahead with the Snow Day Calculator.