Sprinkler Calculator
Lay out a sprinkler system for your lawn. Enter the lawn size and choose a head type, then see how many heads you need, how many zones to split them into and how long to run each zone.
| Detail | Result |
|---|---|
| Total flow if all run | 30 GPM |
| Head spacing | 15 ft |
| Run time per week | 38 min |
| Pipe, rough estimate | 300 ft |
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How Sprinkler Calculator Works
Four quick steps happen behind the screen every time you change a number.
Sets the spacing
Heads are placed one radius apart, so each head reaches the next one. This is called head to head coverage.
Counts the grid
Lawn length and width are divided by that spacing and rounded up, with a head at each corner.
Adds up the flow
The total flow of all heads is compared with your supply to decide how many zones are needed.
Finds the run time
Time comes from the head type and the weekly water you want, so the lawn gets an even inch.
How to Use Sprinkler Calculator
Five quick steps take you from a tape measure to a usable result.
- Measure the lawnWalk the lawn and note the longest length and the widest width.
- Pick a head typeSpray heads suit small lawns, rotors suit large open areas, and rotary nozzles sit in between.
- Enter your water supplyFill a 5 gallon bucket, time it and convert to gallons per minute. Ten GPM is common at home.
- Set the weekly waterOne inch of water per week suits most grass. Hot weeks may need more.
- Read zones and run timeGroup the heads into the zones shown and run each zone for the minutes listed.
Formula Used in Sprinkler Calculator
These are the standard formulas behind every result, so you can check the numbers yourself.
Head grid
r is the radius of the head in feet.
Zones
Only 80 percent of the supply is used to keep pressure steady.
Run time
Rate is the inches of water a head applies in an hour.
Worked example
A 60 ft by 40 ft lawn with 15 ft spray heads needs 5 × 4 = 20 heads. At 1.5 GPM each that is 30 GPM, so with a 10 GPM supply the system needs 4 zones of 5 heads. To apply one inch a week each zone runs about 38 minutes.
Sprinkler Head Chart
Typical radius, flow and water rate for each head type.
| Head type | Radius | Flow per head | Water rate |
|---|---|---|---|
| Spray head | 15 ft | 1.5 GPM | 1.6 in/hr |
| Rotary nozzle | 22 ft | 1.0 GPM | 0.4 in/hr |
| Rotor head | 30 ft | 3.0 GPM | 0.5 in/hr |
These are typical values. Check the label of your own heads for exact numbers.
Sprinklers by Lawn Size
Heads, zones and weekly run time for common lawn sizes with spray heads and a 10 GPM supply.
| Size | Heads | Zones | Min per week |
|---|---|---|---|
| 30 × 20 ft | 9 | 2 | 38 |
| 40 × 30 ft | 12 | 3 | 38 |
| 60 × 40 ft | 20 | 4 | 38 |
| 80 × 50 ft | 35 | 7 | 38 |
| 100 × 60 ft | 40 | 8 | 38 |
Run time gives one inch of water per week.
Common Sprinkler Mistakes
Four slips that throw off the result, and how to avoid them.
Putting every head on one zone
The supply cannot feed them all at once. Split the heads into zones or pressure drops.
Mixing head types in a zone
Sprays and rotors apply water at very different rates. Keep each type in its own zone.
Spacing heads too far apart
If heads do not reach each other, dry patches appear. Place them one radius apart.
Watering a little each day
Short daily runs keep roots shallow. Water deeper and less often.
Tools You Must Know
One number is rarely enough for a yard project. These calculators pair well with this one.
Sprinkler Calculator FAQs
Quick answers before you order materials.
How many sprinkler heads do I need?
Place heads one radius apart in a grid across the lawn. The calculator counts the rows and columns for you.
What is head to head coverage?
It means each sprinkler throws water as far as the next head, so there are no dry gaps.
How many sprinkler zones do I need?
Divide the total flow of all heads by about 80 percent of your water supply, and round up.
How long should I run my sprinklers?
Spray heads need around 35 to 40 minutes a week for one inch. Rotors take longer because they apply water more slowly.
How do I measure my water supply in GPM?
Time how long a 5 gallon bucket takes to fill at an outdoor tap, then divide 300 by the seconds.
Is the Sprinkler Calculator free?
Yes. It is free to use, with no signup, in feet or metres.
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