LIVE WEATHER-AWARE TOOL
Plan watering with the forecast visible—not hidden inside the answer.
Set a weekly water target, reuse a Garden Area if available, load the local seven-day rain forecast and decide how much of that forecast you want to credit before calculating irrigation volume.
Translate millimetres of water into litres your garden can use.
One millimetre of water spread across one square metre equals one litre. A 20 mm target over 10 m² therefore represents 200 litres before any rainfall credit is considered.
The forecast layer shows the next seven days of predicted rainfall for the selected place. Tiny Mustard Seed does not silently subtract that forecast from the irrigation target. The gardener chooses a rainfall credit—either by entering a value or explicitly using the forecast total—so the assumption remains visible and editable.
The remaining irrigation depth is the target depth minus the chosen credit, floored at zero. Multiplying that remaining depth by the watered area produces the planned irrigation litres.
A forecast millimetre is not automatically a usable soil millimetre.
A weather service predicts precipitation for an area, not the exact amount that will become useful water in every bed. A greenhouse roof can exclude rain entirely. Dense foliage can intercept some rain. Sloped or compacted ground can shed water. Intense rain can run off, while lighter rainfall may infiltrate more effectively.
Forecasts can also change before the event occurs. For those reasons, the raw forecast and the amount credited to the watering plan are shown as separate numbers. A user who trusts the full forecast can apply it with one button; a user expecting partial benefit can enter a smaller value.
This separation also makes saved watering plans easier to interpret later because the chosen assumption is recorded alongside the forecast rather than being hidden.
Garden watering calculator FAQ
Does the calculator automatically subtract forecast rain?
No. Forecast rainfall is displayed separately. The irrigation calculation changes only when you explicitly enter a rainfall credit or choose to use the forecast total as that credit.
Why keep forecast rain and credited rain separate?
Forecast rain may miss a specific garden, arrive unevenly, run off, be intercepted by shelter or foliage, or change before it falls. Separating the values makes the assumption visible instead of hiding it inside the result.
How are millimetres converted to litres?
One millimetre of water spread over one square metre equals one litre. The planned irrigation volume is the watered area multiplied by the remaining millimetres after the user-chosen rain credit.
Can I reuse a Garden Area from My Garden?
Yes. A saved Garden Area can provide the area in square metres and show its saved sun, soil and area type so the watering calculation uses the same location name as other garden records.
Should I water whenever the calculator shows a positive volume?
Not automatically. Check actual rainfall and root-zone moisture first. Soil type, mulch, wind, crop stage, containers and plant condition can make the real need different from the planning target.