The formulas
- Emitter line = bed length × lines per bed × beds. Add supply tubing to reach the beds.
- Emitters per line = length in inches ÷ spacing, plus one at the start.
- Total flow = emitters × flow per emitter.
- Gallons for 1 inch = bed area in sq ft × 0.623.
- Time for 1 inch = gallons for 1 inch ÷ flow per bed. All the beds run at once.
How many lines per bed?
Water spreads sideways differently in each soil. Light, sandy mixes need lines closer together, because water moves down more than out. A 4-foot-wide bed usually gets three or four lines, and a 2-foot bed one or two. Tennessee State University Extension notes that emitter spacing affects how water spreads through a bed and that 12 inches is the most common choice for home gardens.
Check it against your water supply
Time how long your tap takes to fill a 1-gallon bucket. Divide 3,600 by the number of seconds to get gallons per hour. If your total flow gets close to this, split the garden into zones. Check the maximum run length for your tubing too, as long lines lose pressure at the far end.
Treat run time as a starting point
The time shown assumes even distribution with no losses. Real needs depend on weather, soil and crops. Use it to set your timer, then check moisture a few inches down and adjust.