How much water does a traveling gun apply?
A traveling gun, also called a hose-reel traveler, pulls a single large sprinkler along a straight path called a travel lane while it sprays a wide circle of water. Because the gun is moving instead of standing still, the amount of water any one spot receives depends on how long the gun's wetted circle passes over it — which comes down to three numbers: how fast water leaves the gun (its flow rate), how far apart the travel lanes are set (lane spacing), and how quickly the cart moves (travel speed).
Put those three together and you get a gross application depth: the average depth of water laid down over the strip on one pass, the same way rainfall or a stationary sprinkler's output is measured in inches or millimeters. It's the number you need before deciding whether one pass is enough, or whether the traveler needs to run the lane again.
This calculator works in the direction most people start from — flow rate, lane spacing and speed in, depth out — and in reverse: tell it the depth you're trying to hit and it solves for the travel speed that gets you there.
Check your permit or nutrient management plan first. If the gun is applying wastewater, effluent or manure, application limits and required setbacks are set by your state agency or Comprehensive Nutrient Management Plan, not by this calculator.
How this traveling gun calculator works
The calculator uses the standard irrigation engineering relationship between a traveling sprinkler's flow rate, the width of ground it waters, and how fast it covers that ground.
Application depth (forward mode)
US units
Depth (in) = 96.3 × Flow rate (gpm) ÷ [Lane spacing (ft) × Travel speed (ft/hr)]
96.3 converts gallons per minute and feet into inches of depth per hour of travel (231 in³ per gallon ÷ 144 in² per ft² × 60 min/hr ≈ 96.3, the standard rounding used in irrigation engineering references).
Metric units
Depth (mm) = 60 × Flow rate (L/min) ÷ [Lane spacing (m) × Travel speed (m/hr)]
One millimeter of water over one square meter is exactly one liter, so the only conversion needed is minutes to hours (×60).
Travel speed (reverse mode)
Rearranging the same formula for speed gives the travel speed needed to hit a target depth:
US units
Travel speed (ft/hr) = 96.3 × Flow rate (gpm) ÷ [Lane spacing (ft) × Target depth (in)]
Example: a 400 gpm gun on a 250 ft lane needs about 154 ft/hr to apply 1.00 in in one pass (96.3 × 400 ÷ 250 ÷ 1.00 = 154.08).
Metric units
Travel speed (m/hr) = 60 × Flow rate (L/min) ÷ [Lane spacing (m) × Target depth (mm)]
Dial equivalent and lane time
Many traveler controllers are set in minutes to pull the hose in 100 ft (or 100 m), not in feet per hour, so the calculator also converts the speed into that form: minutes per 100 units = 6,000 ÷ speed (in units per hour). If you enter a lane length, it also gives the time to finish the lane (lane length ÷ speed) and the area that lane covers (lane spacing × lane length, converted to acres or hectares).
Rounding used on this page
Application depth is shown to 2 decimal places in US units and 1 decimal place in metric, matching the precision the calculation itself carries. Travel speed and the dial equivalent are shown to the nearest tenth below 10, and to the nearest whole unit above it, since traveler speed settings are rarely set more finely than that.
When this calculator isn't the right tool
It's built specifically for a single traveling gun pulled along a straight lane. Use a different tool for:
- Center pivots and linear-move systems, which rotate or move on wheeled towers rather than being pulled by a hose reel. See the center pivot calculator.
- Furrow or flood irrigation, where water moves across the field surface instead of through the air. See the furrow irrigation calculator or the flood irrigation calculator.
- Solid-set or hand-move sprinkler grids, which use sprinkler and lateral spacing rather than a travel lane. See the irrigation application depth calculator.
- Converting a known depth into a volume or vice versa without the travel-lane geometry. See the acre-inches calculator.
Traveling gun calculation examples
A traveler runs a 320 gpm gun on a 200 ft lane spacing at a travel speed of 130 ft/hr, pulling a 900 ft lane.
- Application depth: 96.3 × 320 ÷ (200 × 130) = 30,816 ÷ 26,000 ≈ 1.19 in.
- Dial equivalent: 6,000 ÷ 130 ≈ 46.2 min per 100 ft.
- Time to finish the lane: 900 ÷ 130 × 60 ≈ 415 minutes, or about 6 hr 55 min.
- Area covered: (200 × 900) ÷ 43,560 ≈ 4.13 acres.
The same calculation in metric
A 1,200 L/min gun on a 70 m lane spacing at 45 m/hr, pulling a 300 m lane:
- Application depth: 60 × 1,200 ÷ (70 × 45) = 72,000 ÷ 3,150 ≈ 22.9 mm.
- Dial equivalent: 6,000 ÷ 45 ≈ 133.3 min per 100 m.
- Time to finish the lane: 300 ÷ 45 × 60 ≈ 400 minutes, or about 6 hr 40 min.
- Area covered: (70 × 300) ÷ 10,000 ≈ 2.1 ha.
Both examples use the same relationship: a faster cart or a wider lane spreads the same flow over more ground, so the depth per pass drops.
Setting up and running a traveling gun
Getting a reliable number out of this calculator depends more on measuring your inputs correctly than on the math itself. The formula is exact; the flow rate, lane spacing and speed you feed it usually aren't unless you check them.
Measure the flow rate at running pressure
A gun's flow rate changes with operating pressure, and pressure drops as water travels through the hose reel and the length of lay-flat or hard hose feeding the cart. Reading gpm off a catalog at the pump's pressure, rather than the pressure actually reaching the nozzle, is one of the most common sources of error. If the gun has a pressure-tap fitting, check it directly with a gauge and match that reading to the manufacturer's nozzle chart, or measure flow with a meter or a timed bucket test.
Choosing lane spacing
Lane spacing has to overlap the gun's wetted diameter, not just sit inside your field boundaries. Alabama Cooperative Extension System's guidance for calibrating traveling guns sets spacing at about 70% of the nozzle's wetted throw diameter for uniform coverage. Manufacturers publish their own recommended spacing for each nozzle and pressure combination, and that number should take priority over a general rule when it's available.
Wind narrows a gun's effective throw and skews the pattern downwind, which is why USDA NRCS's sprinkler system conservation practice standard advises against operating traveling sprinklers in winds above 10 mph, with closer lane spacing recommended as wind speed rises. Running at dawn or dusk, when wind is typically calmer, protects both the calculated depth and its uniformity across the strip.
Common mistakes
- Using a nameplate flow rate instead of the running one. Hose friction loss on a long pull can cut pressure — and therefore flow — well below the catalog number.
- Setting lane spacing from the field width instead of the gun's throw. A lane spacing wider than the gun's effective wetted diameter leaves a dry strip between passes that no amount of extra time on either lane will fix.
- Confusing a dial's minutes-per-100-ft setting with the ft/hr this calculator uses. Use the dial equivalent in the result to translate between the two instead of guessing.
- Ignoring soil intake rate. A depth this calculator says is achievable can still run off if it arrives faster than the soil absorbs it, especially on clay or compacted ground; see the soil infiltration rate chart.
How much depth do you actually need?
This calculator tells you what a given setup will apply, not how much your crop needs. Pair it with the crop water requirement calculator to work out a target depth from crop stage and evapotranspiration, then use that target in this tool's reverse mode to find the travel speed that delivers it.
What changes the result
The calculator only knows the numbers you give it. These are the main reasons the real depth in the field can differ from the calculated one.
| Factor | Effect on the result | What to check |
|---|---|---|
| Pressure loss along the hose | Lowers the gun's actual flow rate below its catalog rating, especially on long pulls. | Measure pressure at the gun, not at the pump. |
| Wind | Narrows and skews the wetted pattern; NRCS advises against operation above 10 mph. | Run during calmer hours; tighten lane spacing in wind. |
| Lane spacing vs. wetted diameter | Spacing wider than the gun's effective throw leaves an under-watered strip between lanes. | Check spacing against the manufacturer's chart, not just field width. |
| Travel speed consistency | A cart that speeds up, slows down or stalls applies uneven depth along the lane. | Watch the winch or reel for slipping cable or a worn turbine drive. |
| Nozzle wear or wrong size | A worn or mismatched nozzle changes flow rate at the same pressure. | Compare measured flow against the chart for the installed nozzle. |
| Soil intake rate | A depth applied faster than the soil absorbs it runs off instead of soaking in. | Compare the application rate to your soil's infiltration rate. |
Of these, pressure loss and wind are the two most likely to make a well-calculated depth wrong in practice, since both change the gun's actual output rather than anything you enter into the calculator.
Frequently asked questions
How is the application depth of a traveling gun calculated?
The depth for one pass equals a constant times the gun's flow rate, divided by the lane spacing times the travel speed: in US units, Depth (in) = 96.3 × Flow rate (gpm) ÷ (Lane spacing (ft) × Travel speed (ft/hr)). The constant converts gallons and feet into inches of depth over the strip the gun waters. Slow the cart down or narrow the lane spacing and the same flow rate lays down more water; speed it up or widen the spacing and it lays down less.
How do I find my traveling gun's actual flow rate?
The most reliable way is to read the gun's nozzle size and operating pressure off the manufacturer's performance chart, which lists gallons per minute for each combination. Many guns have a small pressure-tap fitting on the body where a gauge can confirm the running pressure right at the nozzle. A flow meter on the supply line, or a bucket-and-stopwatch test at a hydrant, both work if you don't have the gun's chart. Use the actual operating pressure, not the pressure at the pump, since friction loss through the hose reel can be substantial.
How should I set the travel lane spacing?
Lane spacing should overlap the gun's wetted diameter enough that no dry strip is left between passes. Alabama Cooperative Extension recommends spacing lanes at about 70% of the nozzle's wetted throw diameter for uniform coverage. Wind distorts the pattern and narrows the effective throw, so USDA NRCS's sprinkler system standard advises against operating traveling sprinklers in winds above 10 mph and calls for closer spacing as wind increases. Check the gun manufacturer's own spacing table first, since throw diameter varies by nozzle, pressure and trajectory angle.
Why does travel speed change the application depth so much?
Depth is inversely proportional to speed: the formula divides by travel speed, so cutting the speed in half doubles the depth, and doubling the speed halves it. That's because a slower cart spends more time delivering water to each square foot of the strip. Travel speed is also the easiest setting to change on most travelers, which is why this calculator's reverse mode solves for the speed needed to hit a target depth instead of the other way around.
What travel speed should I use to apply a certain amount of water?
Switch this calculator to "Find travel speed," enter the gun's flow rate and lane spacing, then enter the depth you want applied in one pass. The result is the speed that produces that depth with your numbers. Check it against the range of speeds your traveler's reel or winch actually offers: most travelers have several fixed speeds or a limited variable range, so an unusually fast or slow result may not be achievable and calls for a different lane spacing instead.
Does a wider lane spacing always mean less water applied?
Yes, at the same flow rate and travel speed, widening the lane spacing spreads the same volume of water over a bigger strip, so the calculated depth drops. But spacing that's too wide leaves a dry band between adjacent passes because it goes beyond the gun's effective wetted diameter. Use the manufacturer's spacing recommendation for the nozzle and pressure you're running, not just whatever depth this calculator shows for a given spacing.
Does wind affect how much water actually reaches the ground?
Yes, more than for most sprinkler types, because a traveling gun throws water high and far. A 2026 field and simulation study published in the journal AgriEngineering found the uniformity coefficient of a big-gun sprinkler fell from about 84% in calm conditions to under 30% with a roughly 6 m/s (13 mph) headwind. This calculator assumes the gun's full wetted diameter reaches the ground as designed; in real wind, less water lands within the intended strip than the calculated depth suggests.
Can I use this for wastewater, effluent or manure travelers, not just clean irrigation water?
The depth, speed and lane-spacing relationship is a physical formula that applies to any traveling gun, whatever is in the water. What changes for wastewater, effluent or manure is everything around the calculation: nutrient loading limits, required setbacks from wells and waterways, and permit or nutrient-management-plan requirements, which vary by state and by operation. Check your Comprehensive Nutrient Management Plan or state agency requirements before using a calculated depth to set an application rate for anything other than clean irrigation water.
Who built and checked this calculator
Licensed Professional Engineer and Irrigation Association Certified Irrigation Designer with more than 20 years in irrigation design, system auditing and landscape water management. Full profile
How this page was checked
- Formula, unit conversions and all five test cases verified by hand against the source equations below.
- Lane-spacing and wind guidance checked against the extension and NRCS sources below.
- The reverse-mode (speed-from-depth) calculation was cross-checked against the forward calculation for the same inputs.
Sources
- Irrigation Systems Management (AET 021), Section 12.5.3: Operational Characteristics. Workforce LibreTexts.
- North Carolina Department of Environmental Quality. Math Formulas for Surface Irrigation Systems.
- Alabama Cooperative Extension System. Calibrating Traveling Guns for Slurry Irrigation (ANR-0925).
- USDA Natural Resources Conservation Service, North Carolina. Conservation Practice Standard: Sprinkler System (Code 442), 2015.
- Fonseca Elias de Oliveira, H., et al. "Water Distribution Uniformity of Traveling Gun Sprinklers: Day–Night Wind and Towpath Alignment." AgriEngineering, 2026. doi.org/10.3390/agriengineering8030102.