Free calculator
Water Butt Calculator
Compare roof rainfall yield, storage, fill rainfall and garden watering demand without treating annual yield as tank size.
Open calculator →Garden project hub
Watering, irrigation & rainwater
Catch rain, store it, estimate the litres the garden needs, then translate a known flow rate into time.
Use the right quantity tool
Calculators for watering, irrigation & rainwater
Estimate rainfall collection, storage, garden demand and irrigation runtime without pretending to design a hydraulic system.
Free calculator
Garden Irrigation Calculator
Calculate watering litres, runtime, delivered volume and nominal drip-emitter flow from user-entered rates.
Open calculator →Free calculator
Garden Area Calculator
Measure lawns, beds and awkward garden shapes in square metres before moving into a material or planting calculator.
Open calculator →Before you order
Keep the project decisions separate from the arithmetic
Rainfall becomes litres
One millimetre of rain over one square metre is one litre before collection losses. The Water Butt Calculator applies an editable collection efficiency and keeps annual yield separate from sensible tank capacity.
Watering demand also uses area × depth
A selected watering depth in millimetres translates directly to litres per square metre. The site does not prescribe one universal depth because plants, soil, weather and season change the requirement.
Runtime depends on known flow
Once the required litres are known, Irrigation Calculator divides by the actual system flow. Manufacturer-rated emitter flow is useful planning data, but pressure loss and pipe sizing sit outside this homeowner calculator.
Supporting guidance
Read the guide when the difficult part is choosing the input
Practical guide
What Size Water Butt Do I Need?
Think about roof catchment, rainfall timing, storage turnover and garden demand before choosing capacity.
Read guide →Practical guide
Garden Irrigation Planning in Litres
Translate area, selected watering depth and known system flow into a transparent water-volume and runtime plan.
Read guide →Continue the project
Useful next routes
Move to the next quantity only when it describes a genuinely different part of the job.
Choose storage sensiblyUnderstand roof catchment, rainfall timing and storage turnover.Plan watering in litresTranslate area, selected depth and flow into a runtime plan.Litres per square metreUse the depth reference for the same 1mm × 1m² relationship.Ponds & waterGo to pond volume and liner sizing when the project is a pond rather than irrigation.