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A rain gauge should not be placed where trees, buildings, roofs, sprinklers, hard surfaces, or strong wind can change how much water reaches the opening. The goal is to measure rain falling from the sky, not water that has been blocked, blown away, splashed in, or added from another source.
For most homes, a level spot in an open yard works well. Keep the gauge away from nearby obstacles while avoiding rooftops and other exposed, windy locations.
Do Not Put a Rain Gauge Under a Tree
Trees are one of the most common causes of bad rain gauge readings.
Branches and leaves can catch rain before it reaches the gauge. During heavier storms, water can also drip from leaves and branches into the gauge. Either problem can make the reading different from the rainfall that actually fell over the area.
Trees also change the wind around the gauge.
Do not place the gauge:
- Directly under branches
- Beside a tree trunk
- Under a tree canopy
- Where growing branches may eventually reach over the gauge
CoCoRaHS recommends keeping gauges a reasonable distance from obstacles. Its home-observer guidance gives an example of placing a gauge about 80 feet from a 40-foot tree. In other words, aiming for roughly twice the obstacle's height is a useful target when your yard allows it.
You may not have that much room in a small yard. In that case, choose the location with the clearest view of the sky and the least interference.
Do Not Put It Next to a House or Other Building
A wall, shed, garage, or house can block wind-driven rain coming from one direction.
The opposite problem can happen too. Wind flowing over a roof and around walls creates turbulence. That disturbed airflow can carry raindrops over the gauge instead of into it.
The National Weather Service warns against locating precipitation gauges close to isolated obstructions such as buildings and trees because they can deflect precipitation and create turbulent airflow.
Avoid spots beside:
- Houses
- Garages
- Sheds
- Barns
- Tall privacy walls
- Large garden structures
Moving the gauge several feet away from a wall is better than mounting it directly against the building, but greater clearance is usually better.
Do Not Put a Rain Gauge Under Roof Eaves
An eave or roof overhang can directly block rainfall.
It can also concentrate roof runoff. Water dripping from an eave may enter the gauge during or after a storm and give you a reading that is much too high.
Keep the gauge far enough away that roof runoff, dripping water, and splash cannot reach it.
This is especially important if you are comparing gauge rainfall with the amount of water collected by a rain barrel or cistern. Your gauge should measure rainfall itself, not runoff from the roof.
Avoid Mounting It on the Roof
A roof may seem ideal because nothing blocks the sky. In practice, it can be a poor rain gauge location.
Roofs are exposed to stronger wind. Air moving around roof edges, ridges, vents, and other features becomes turbulent. This can reduce the amount of rain caught by the gauge.
National Weather Service siting guidance specifically advises against elevated locations such as building tops because wind and turbulence can cause precipitation measurement errors.
A ground-level yard location is normally better.
It is also easier and safer to empty, inspect, clean, and level a gauge without repeatedly climbing onto a roof.
Do Not Put It Near a Sprinkler
A rain gauge cannot tell the difference between rainfall and irrigation water.
A lawn sprinkler that reaches the gauge can make a small rainstorm look much larger than it really was. It can even produce a rainfall reading on a completely dry day.
CoCoRaHS specifically recommends keeping gauges away from sprinklers and other artificial sources of precipitation.
Also watch for:
- Garden sprinklers
- Irrigation rotors
- Hose-end sprinklers
- Misting systems
- Automatic watering systems
Check the sprinkler's full spray pattern, including what happens when wind carries the spray farther than usual.
Do Not Put It Where Water Can Splash Into It
Rain hitting a nearby surface can bounce droplets into the gauge.
Possible splash sources include:
- Concrete patios
- Decks
- Large rocks
- Roof surfaces
- Wide fence posts
- Tables
- Outdoor equipment
This extra water can raise the measured rainfall.
The gauge should be mounted so that nearby surfaces cannot easily splash water upward into its opening. CoCoRaHS specifically advises avoiding locations where heavy rain could splash into the gauge.
A narrow stand-alone post is usually better than setting the gauge on a broad horizontal surface.
Avoid Deck Railings
A deck railing is convenient, but it may not provide a good measurement location.
The house can affect rainfall and airflow. The deck surface may create splash. Railings and nearby structures can also disturb wind.
CoCoRaHS placement guidance lists decks among locations to avoid.
If a deck is your only practical location, understand that your readings may be less representative than readings from a properly placed gauge in the yard.
Do Not Put It in a Wind Tunnel
Avoid narrow spaces where wind is funneled between structures.
Consider placement effects on household rainfall measurements to understand installation planning for dependable ongoing service.
Examples include:
- Between two buildings
- Between a house and tall solid fence
- Narrow side yards
- Passages between sheds
- Openings where prevailing winds are concentrated
Fast, turbulent air can carry raindrops past the gauge opening.
The National Weather Service advises against areas with channeled winds and notes that greater wind exposure generally produces greater precipitation measurement error.
But Do Not Choose an Extremely Exposed Location Either
A rain gauge needs a clear view of the sky, but that does not mean the highest and windiest spot on your property is best.
A completely exposed hilltop, rooftop, tower, or similar location may experience enough wind to reduce the gauge's catch.
The ideal arrangement is somewhat counterintuitive: the gauge should be clear of nearby obstacles but not unnecessarily exposed to extreme wind.
National Weather Service guidance describes a good site as one with reasonably uniform protection from distant surroundings rather than one immediately beside a single large obstruction.
For a normal backyard, concentrate first on finding level ground with open sky and good clearance from trees and buildings.
Avoid Places That Are Hard to Maintain
Do not install the gauge somewhere that makes routine access difficult.
Poor choices include locations:
- Behind dense shrubs
- Inside thorny landscaping
- On an unsafe slope
- Behind a locked or difficult gate
- Where you need a ladder for every reading
- Where pets or livestock regularly knock into it
You need to be able to inspect the opening, remove debris, empty the gauge, and confirm that it remains level.
A theoretically perfect location is not very useful if you cannot maintain the gauge.
Do Not Put It Where the Gauge Can Be Easily Knocked Over
A gauge that tilts will not collect rain properly.
Avoid locations where it is likely to be hit by:
- Lawn mowers
- String trimmers
- Children playing
- Pets
- Livestock
- Vehicles
- Garden carts
Also avoid attaching the gauge to a post that moves or leans.
The opening at the top needs to stay level. CoCoRaHS specifically includes leveling the top of the gauge among its basic mounting requirements.
What Does a Good Rain Gauge Location Look Like?
For many homes, a good location is a relatively open part of the yard with the gauge mounted securely on a narrow post.
Look for a spot that:
- Has a clear view of the sky
- Is well away from trees and buildings
- Cannot receive sprinkler water
- Is away from roof runoff
- Has little chance of splash entering the opening
- Is not on a rooftop or other highly exposed location
- Is easy to reach for readings and cleaning
- Allows the gauge opening to remain level
For common manual gauges, CoCoRaHS recommends mounting the gauge about 2 to 5 feet above the ground, with its top extending above the mounting post.
If you are reporting measurements to a formal weather-observation network, follow that network's exact installation requirements rather than general backyard guidance.
Why Rain Gauge Placement Matters for Rainwater Harvesting
Rainfall measurements can help you understand how much water your roof may collect.
But a poorly placed gauge can make your calculations misleading.
For example, suppose a gauge under a tree records less rain than actually fell. You might conclude that your rainwater harvesting system is collecting unusually large amounts of water.
A sprinkler-contaminated gauge can create the opposite problem. It may suggest that much more rain fell than actually reached the roof.
Remember that rainfall depth and tank volume are different measurements. A rain gauge tells you how much rain fell at one location. The amount entering a rain barrel, IBC tote, or cistern also depends on roof area, losses, overflow, first-flush diversion, leaks, and other parts of the collection system.
A well-placed gauge gives you a much better starting point.
Frequently Asked Questions
How far should a rain gauge be from a tree?
More distance is generally better. A useful home-observer target is to place the gauge about twice as far from an obstacle as that obstacle is tall when your property allows it. For example, CoCoRaHS gives an example of keeping a gauge about 80 feet from a 40-foot tree. Small yards may require a compromise.
Can I put a rain gauge next to my house?
It is better to move it away from the house. Walls and roofs can block wind-driven rain and create turbulent airflow that changes how much water enters the gauge.
Can a rain gauge be mounted on a roof?
A roof is generally a poor location for a standard rain gauge. Elevated roofs experience stronger and more turbulent wind, which can reduce the amount of precipitation caught. Roof access also makes routine maintenance less convenient and may create unnecessary fall risk.
Can I put a rain gauge on my deck?
A yard location is usually better. Decks can expose the gauge to splash, nearby building effects, and disturbed airflow. If the deck is the only available location, your readings may be less representative.
Should a rain gauge be in full open sky?
The opening should have a clear view of the sky and should not sit beneath trees, eaves, or nearby structures. However, an extremely windy elevated location is also undesirable. Look for an unobstructed yard location without excessive wind exposure.
Can I put a rain gauge near my garden sprinkler?
No. Sprinkler water can enter the gauge and be recorded as rainfall. Place the gauge outside the sprinkler's normal spray area and allow extra clearance for wind-blown spray.
Does a rain gauge need to be level?
Yes. The opening should be level so the gauge catches rain as intended. Check it after installation and occasionally afterward, especially if the post can shift in soft or wet soil.
