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Garden Irrigation Calculator — Zones, Heads & Pipe
Calculate sprinkler head count, head-to-head spacing, irrigation zones, total flow demand, water per session and pipe length for a garden irrigation system.
Measure at your outdoor tap
Total pipe needed (0 = rough auto estimate — measure your actual run)
50% of diameter = head-to-head (recommended); 60% max; 45% in wind
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How We Calculate This
This calculator determines the number of sprinkler heads, irrigation zones, pipe requirements and water consumption for a garden watering system.
Head count
Heads = Garden Area / (Spacing²)
Heads are laid out on a grid for head-to-head coverage, where the spacing equals the radius (50% of the throw diameter). The area each head covers is the grid cell — spacing squared — not the full circle, because the circles overlap by design. For a 4m-radius pop-up, spacing is 4m and each head covers a 16 m² cell.
Zone calculation
Zones = Total Flow Demand / Available Flow Rate (rounded up)
Each zone runs independently. Because the zones run one after another and every head runs once, the water used in a full watering session is Total Flow Rate × Runtime.
Frequently Asked Questions
The number of heads per zone is limited by your available water flow rate. A 4m full-circle pop-up spray head uses about 10 L/min (Rain Bird MPR data: a 12ft/3.66m full-circle nozzle draws 2.6 GPM ≈ 9.8 L/min at 30 psi), so with a typical UK mains flow of 20 L/min you can run about 2 full-circle pop-ups per zone — more if you use lower-flow half or quarter-arc nozzles, which draw proportionally less. Rotor heads use roughly 15-20 L/min each, so often just one per zone. Drip lines use far less (around 2 L/hr per emitter) so many can run on one zone. Always measure your actual flow rate at the tap.
For most domestic garden irrigation, 25mm MDPE pipe is the standard choice. It handles flow rates up to 30 L/min with acceptable friction loss. For longer runs (over 30m) or higher flow systems, use 32mm. 20mm is adequate for small drip-only systems. Use compression fittings for MDPE connections.
Zones = Total flow demand / Available flow rate, rounded up. If you have 8 full-circle pop-up heads (about 10 L/min each = 80 L/min total) and 20 L/min available, you need 4 zones (80 ÷ 20 = 4). Each zone runs separately, controlled by a timer or controller. Keep zones with similar head types together — don't mix pop-ups and drip on the same zone.
For "head-to-head" coverage, space sprinklers at 50% of their throw diameter — which equals the radius — so the spray from each head just reaches its neighbours. A pop-up with a 4m radius (8m diameter) should therefore sit about 4m apart, up to a 4.8m absolute maximum (60% of diameter). In the UK, wind reduces the effective throw, so move heads closer — around 45% of diameter (about 3.6m). Stretching beyond head-to-head spacing leaves dry spots between heads.
If your mains pressure is above 2 bar and flow rate above 15 L/min, you can run a small irrigation system directly from the mains (via a double-check valve to comply with Water Regulations). For larger systems or low-pressure supplies, a pump drawing from a water tank or rainwater harvester is needed. A booster pump adds around £200-400.
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Last updated: March 2026
Verified against UK standards · estimates only, confirm with your supplier.