Rainfall Volume Planning
Rain depth looks small on a gauge. It becomes large volume on a roof, patio, field, or garden bed. This calculator turns inches of rain into gallons. It helps you size barrels, tanks, drains, and irrigation plans. The tool starts with rainfall depth. Then it multiplies that depth by catchment area. A standard factor changes inch square feet into gallons.
Why Area Matters
Area controls the final volume. One inch on a small shed gives modest storage. One inch on a large roof can fill several barrels. That is why the area unit field accepts many common choices. You can enter square feet, square meters, acres, yards, inches, or hectares. The page converts every option to square feet before calculating.
Runoff And Efficiency
Real collection is never perfect. Roofing material, slope, first flush diverters, gutters, leaks, and splash loss reduce useful water. The runoff coefficient handles surface behavior. A smooth roof can use a higher value. Soil, turf, or rough ground should use a lower value. Collection efficiency handles system loss after runoff. Use it for gutter capture, filter loss, and tank overflow. Fixed losses can remove a known number of gallons.
Better Decisions
The result gives gross gallons and adjusted gallons. It also shows liters, cubic feet, acre feet, and flow per hour when duration is entered. Tank fill percentage helps compare the storm with storage space. Use the table for quick examples. Use CSV export for spreadsheets. Use PDF export for job notes or client records.
Practical Tips
Measure roof length and width carefully. Break complex roofs into rectangles. Add their areas before entry. Use local rainfall records for design storms. Use small runoff values for gardens because water infiltrates soil. Use higher values for metal, tile, or asphalt roofs. Leave extra tank capacity for heavy storms. Check overflow routing before rain arrives. This avoids pooling near walls and foundations. Recalculate when gutters, tanks, or surface materials change. Small changes in area or efficiency can shift the final gallon estimate. Keep one saved result for each catchment zone. For seasonal planning, repeat the calculation with average monthly rainfall. Compare totals with outdoor water demand. This shows when storage may run short during dry summer weeks.