Calculator
Example Data Table
These sample rows show typical inputs and resulting weekly depth. Values are illustrative and vary by soil, sun, wind, and plant stage.
| Area | Events/week | Volume/event | Efficiency | Rainfall | Weekly inches (approx) |
|---|---|---|---|---|---|
| 250 sq ft | 3 | 10 gal | 70% | 0.25 in | 0.79 in |
| 500 sq ft | 4 | 12 gal | 65% | 0.00 in | 0.40 in |
| 30 sq m | 3 | 40 L | 75% | 8 mm | 0.39 in |
Formula Used
- Depth from volume: inches = gallons ÷ (areasqft × 0.623)
- Area conversions: 1 m² = 10.7639 ft², 1 acre = 43,560 ft², 1 yd² = 9 ft²
- Volume conversions: 1 liter = 0.264172 gallons, 1 m³ = 264.172 gallons
- Effective irrigation: effective = applied × (efficiency% × (1 − runoff%))
- Total weekly depth: total inches = irrigation inches + rainfall inches
How to Use This Calculator
- Enter your garden area for the zone you water together.
- Select the irrigation method that matches your data source.
- Add rainfall for the week using inches or millimeters.
- Set efficiency and runoff loss to estimate root-zone water.
- Press calculate, then compare the result to the suggested range.
Weekly Water Planning Guide
1) Why Weekly Inches Matter
Plant roots respond to the total depth of water delivered during a week, not just one irrigation day. Tracking inches lets you compare rainfall with irrigation on the same scale. Many gardens perform well around 0.8–1.5 inches per week, while hot weeks, wind, and full sun can increase demand. This calculator converts mixed inputs into one clear weekly depth.
2) Turning Volume Into Depth
Depth depends on area. One inch of water spread over one square foot equals about 0.623 gallons. If you know gallons (or liters), the calculator divides by area to estimate inches delivered. This is useful for drip zones with a flow meter, tank refills, or pump logs. Larger zones require more volume for the same depth, which is why area accuracy is critical.
3) Efficiency and Runoff Adjustments
Not all applied water reaches the root zone. Sprays can drift, drip lines can leak, and uneven coverage leaves dry spots. Efficiency in the 60–85% range is common in real gardens. Runoff losses rise on slopes, compacted soil, or when watering too fast. By applying these factors, the calculator estimates effective water, helping prevent both overwatering and stress.
4) Adding Rainfall Correctly
Rain gauges and weather apps often report millimeters. Since 25.4 mm equals one inch, the calculator converts mm to inches and adds it to effective irrigation. If rainfall was intense and short, some water may run off; reflect that using the runoff loss field. For better decisions, record rainfall by week and compare it to your target range.
5) Interpreting the Result
Use the total weekly inches to tune your schedule. If you are below the suggested range, add a small depth and split it across more days for sandy soils. If you are above range, reduce event volume or frequency. Recheck after heat waves, new plantings, or mulching, and verify with soil moisture at 2–4 inches depth.
FAQs
1) What does “weekly inches” represent?
It is the effective depth of water delivered to the garden during a week, combining irrigation and rainfall. It helps compare all water sources using a single unit.
2) Why does area change the result so much?
Depth is volume divided by area. The same gallons spread over a bigger area produces fewer inches, so accurate zone area is essential for meaningful comparisons.
3) How should I choose an efficiency value?
Use 70% as a practical starting point. Raise it if distribution is uniform and wind is low, and lower it for sprays with drift, leaks, or uneven coverage.
4) Should I include rainfall from a single storm?
Yes, but consider runoff. If the storm caused puddling or water flowing away, increase runoff loss to reflect the portion that did not soak into the root zone.
5) How do I measure weekly irrigation depth at home?
Place several straight-sided cups in the watered area, run one full cycle, and average the collected depth. Multiply by events per week for weekly depth.
6) What weekly inches are typical for vegetables?
Many vegetable beds perform well around 1.0–2.0 inches per week in warm periods, depending on soil type, mulch, canopy size, and local weather.
7) Can this replace a soil moisture check?
No. Use it to plan and compare weeks, then confirm by checking soil moisture 2–4 inches deep. Adjust schedules based on plant response and soil feel.