Rain Gun & Spacing & Coverage
Throws a wide circle
“One accepted answer here saves a hundred people an hour each.
Enter throw radius, flow and pressure to get gun spacing, the wetted area per gun, the precipitation rate and how many guns per acre and hectare.
Enter your gun
Next: space guns ~30 m apart in a grid; if the 6.7 mm/hr rate exceeds your soil's intake, move the gun more often or use a smaller nozzle.
Throw radius depends on nozzle and pressure; wind distorts the pattern — reduce spacing in windy sites.
Rain gun coverage — key facts
- Wetted area
- π × radius²
- Spacing
- ≈ 60% of wetted diameter
- Precip rate
- flow L/min × 60 ÷ grid area
- Design rule
- precip rate < infiltration rate
- Throw radius
- set by nozzle & pressure
- Wind
- distorts the pattern
- Guns/acre
- acre ÷ grid area per gun
- Privacy
- Runs in your browser; nothing uploaded
One gun, a big wet circle
A rain gun is the heavy hitter of sprinkler irrigation: a single high-pressure jet sweeps a large circle, so a few guns can water a whole field with little pipework. The geometry is simple — the wetted area is π times the throw radius squared — but the design isn't about one circle, it's about how the circles overlap. Space guns at roughly 60% of the wetted diameter and the gaps fill in evenly; space them too far apart and you get dry stripes between them.
This tool turns your throw radius and flow into a working layout — gun spacing, the wetted area per gun, the precipitation rate in mm/hour, and the number of guns per acre and hectare. The precipitation rate is the figure that matters most: keep it below your soil's infiltration rate or water runs off instead of soaking in. Remember throw depends on nozzle and pressure, and wind distorts the pattern. Pair it with the Sprinkler System, Soil Infiltration and Pump tools to design the full set.
Space for overlap
Set guns at ~60% of the wetted diameter.
Avoid runoff
Keep the precip rate below infiltration.
Size the system
Guns per acre and hectare for your layout.
Plan the pump
Flow per gun shows the capacity you need.
Frequently Asked Questions
What is a rain gun?+
A rain gun is a large, high-pressure rotating sprinkler that throws a single big jet of water in a circle, wetting a much larger area than ordinary sprinklers. One gun can cover a wide radius, which makes guns popular for irrigating field crops, fodder and orchards quickly with relatively little pipework.
How do I calculate the area a rain gun covers?+
A rotating gun wets a circle, so the area is π × radius². If the throw radius is 25 m, the wetted area is about 3.14 × 25² ≈ 1,963 m². The tool computes the wetted area per gun from your throw radius so you can see how much ground one gun handles.
How far apart should rain guns be spaced?+
Space guns at about 60% of the wetted diameter so adjacent circles overlap enough for even application. If the wetted diameter is 50 m, set the guns roughly 30 m apart. The tool gives this spacing directly, which you can use along the lateral and between laterals in a grid.
What is the precipitation rate?+
The precipitation rate is the depth of water applied per hour — flow (L/min) × 60 ÷ the grid area each gun serves, expressed in mm/hour. It tells you how fast water lands; the calculator reports it so you can compare it against your soil's intake rate.
Why must the precip rate stay below infiltration?+
If water lands faster than the soil can absorb it, the excess runs off or ponds, wasting water and causing erosion. Keep the precipitation rate below the soil's infiltration rate. If the gun applies too fast, widen the spacing, drop the flow or move the gun more often.
How many rain guns do I need per acre?+
It depends on the area each gun serves at your chosen spacing. The tool divides an acre (and a hectare) by the per-gun grid area to give guns per acre and per hectare, which helps you plan how many guns, laterals and how much pump capacity you need.
What sets the throw radius?+
Throw radius depends on the nozzle size and the operating pressure at the gun — bigger nozzles and higher pressure throw farther. Manufacturers publish radius-versus-pressure charts; use the figure for your nozzle and pressure rather than the maximum, which assumes ideal conditions.
How does wind affect a rain gun?+
Wind distorts the circular pattern, shortening the throw downwind and skewing the wetted shape, which hurts uniformity. In windy areas reduce the spacing, irrigate in calmer parts of the day, or use lower-trajectory nozzles. The clean π r² coverage assumes little or no wind.
Are guns suited to all crops and soils?+
Guns apply large droplets at a high rate, which can damage delicate crops and seal or erode light or crusting soils. They suit robust field and fodder crops on soils with good infiltration. For sensitive crops or slow soils, sprinklers or drip are gentler — see the Sprinkler System and Drip tools.
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