Rain gauges collect rain so you can measure how much fell during a storm. With an adult supervising, you can turn a clear container into a useful weather instrument and keep a rainfall record for your home, classroom, or science project.
What You Will Need
Gather the materials before beginning. An adult should help choose the container, use any sharp tools, and decide where the gauge will be placed.
- A clear, straight-sided plastic container, such as a wide-mouth bottle or food container
- A ruler marked in millimeters and centimeters
- Waterproof marker or masking tape
- Scissors, a craft knife, or a hole punch, used only by an adult
- A flat tray, brick, or small board to make a stable base
- A few clean pebbles for weight
- A notebook or weather-recording sheet
- A watch or clock
- Optional: a funnel, rubber band, permanent labels, and a thermometer
A container with vertical sides is easiest to read. Avoid a container that narrows sharply toward the bottom, because the same amount of rain will produce different depths at different parts of the container. A clear plastic container is generally safer than glass outdoors and is less likely to break if it falls.
Before using the container, wash it thoroughly and remove food residue. Do not use a container that held cleaning chemicals, fuel, medicine, or any other substance that could be harmful. Never drink from the rain gauge after it has been outside, even if the water looks clean.
Safety First: Work With an Adult
This activity is simple, but supervision still matters. An adult should handle cutting, drilling, or modifying the container. If a sharp edge is created, it must be covered, smoothed, or replaced with a different container.
Follow these safety rules:
- Build the gauge on a table or floor away from traffic and pets.
- Wear eye protection if an adult cuts or drills plastic.
- Do not use a glass jar if a plastic container is available.
- Keep hands away from blades and ask before touching tools.
- Place the finished gauge where it will not block a walkway or become a tripping hazard.
- Do not stand outside during lightning, strong wind, hail, or dangerous weather.
- Wash your hands after handling rainwater, soil, or outdoor surfaces.
Rainwater can contain dust, pollen, insects, bird droppings, or other contamination. The gauge is for observing weather, not for collecting drinking water. An adult should empty and rinse it regularly.
Build the Rain Gauge
1. Choose and prepare the container
Select a clear container with a flat bottom and sides that remain as straight as possible from the bottom to the top. A container about 10 to 20 centimeters tall works well for ordinary rainfall. It should be wide enough that small leaves or splashes do not make the measurement unreliable.
Remove the lid, label, and any loose parts. Dry the outside so tape and marker will stick. If the container has a curved or uneven bottom, place a few pebbles inside it later and begin measuring above the pebbles. For the most accurate beginner setup, choose a container with a flat interior bottom instead.
2. Make a measuring scale
Place the ruler vertically against the outside of the container. The zero mark should line up with the inside bottom where the water will begin. Mark several lines on the outside using waterproof marker or small pieces of tape.
For example, mark:
- 0 millimeters at the starting level
- 5 millimeters
- 10 millimeters, or 1 centimeter
- 15 millimeters
- 20 millimeters, or 2 centimeters
- Additional marks up to the container’s height
Use millimeters when recording rainfall because weather measurements are commonly reported that way. Remember that 10 millimeters equals 1 centimeter. If the container is too narrow for a ruler to sit directly beside the water, tape a paper scale to the outside, but protect the paper with clear tape so it does not become soggy.
3. Add stability
The gauge must remain upright. Put it on a flat tray, board, or brick. If wind could knock it over, place a few clean pebbles around the outside or inside the bottom. Do not fill the container so much with stones that they take up a large portion of the collecting space.
An adult can attach the container to a heavier base with outdoor tape or place it inside a larger plant pot filled with sand. The rain must still be able to fall freely into the opening. Do not cover the top with a lid or stretch plastic across it.
4. Optional: add a funnel
A funnel can help guide rain into a narrow container, but it changes how the instrument works. The funnel’s opening collects rain over a larger area than the container itself, so the scale must be calibrated for that setup. For a first project, a wide container without a funnel is simpler and easier to interpret.
If an adult chooses to use a funnel, it should fit securely and remain centered. Keep the funnel clean and check that water flows freely through it. Do not assume that the ordinary ruler scale is accurate after adding a funnel.
Place the Gauge Correctly
Location is one of the most important parts of the experiment. Put the gauge outdoors in an open area where rain can fall into it without being blocked or redirected.
A good location is:
- Away from roofs, gutters, trees, fences, walls, and tall plants
- On level ground or a level platform
- Clear of sprinklers and dripping air-conditioning units
- Easy to reach without walking into traffic, deep mud, or thorny plants
- Stable enough that wind will not tip it over
Keep the opening several centimeters above the ground if splashing from soil could enter the container. At the same time, do not place it on a high wall or roof where wind may blow rain over the opening. If the only available location is near a building or tree, write down that limitation because the reading may not represent rainfall across the whole area.
An adult should inspect the location before storms begin. Never go outside specifically to check the gauge during lightning or other dangerous conditions. Wait until the weather is safe.
Measure Rainfall
Choose a regular observation time, such as once each morning. A consistent schedule makes your records easier to compare. If a storm produces heavy rain, the container may fill or overflow before the next observation, so an adult can help check it when conditions are safe.
To read the gauge:
- Look at the water level without moving the container if possible.
- Place your eyes level with the water surface.
- Read the bottom of the curved surface, called the meniscus, rather than the upper edges.
- Record the value in millimeters.
- Note the date, time, weather conditions, and any unusual events.
- Empty and rinse the gauge after recording, unless you are measuring rainfall over a defined period.
A simple record might look like this:
| Date | Time read | Rainfall | Weather note |
|---|---|---|---|
| April 8 | 8:00 a.m. | 6 mm | Light rain overnight |
| April 9 | 8:00 a.m. | 0 mm | Cloudy, no rain |
| April 10 | 8:00 a.m. | 18 mm | Heavy afternoon storm |
If you want to measure rainfall for a particular storm, write down when the container was emptied, when the rain began, and when you took the final reading. Empty the gauge before the storm starts so the measurement does not include older water.
Improve the Accuracy of Your Results
A homemade rain gauge is useful for learning, but it will not be as precise as a professional instrument. You can still make better measurements by controlling the setup.
Use the same container and location throughout the investigation. Keep the gauge upright and check the scale against a real ruler. Read the water at eye level. If the container is marked only every 5 millimeters, record an estimate between marks, such as 7 or 8 millimeters, but be consistent about how you estimate.
Take repeated readings over several days. A single storm may be unusual, while a longer record shows patterns more clearly. You can calculate a weekly total by adding the daily measurements, as long as the gauge was emptied between readings and did not overflow.
For comparison, place a second identical gauge in another open location, such as a school garden and a yard. Use the same reading time and method. Differences may reveal how buildings, trees, slope, or wind affect local rainfall. Do not expect two locations to produce exactly the same reading.
Troubleshooting Common Problems
The gauge tipped over
Move it to a more sheltered, level place and add a heavier base. Do not shelter it so much that a roof, wall, or tree blocks the rain. If water spilled, mark that observation as incomplete rather than guessing the missing amount.
The container overflowed
The storm delivered more rain than the gauge could hold. Use a taller container, check it more often during safe weather, or create a separate high-rainfall scale. You cannot calculate the amount that overflowed unless you have another reliable measurement.
The reading seems too high
Look for splashing from the ground, water dripping from a roof or plant, or a sprinkler nearby. Move the gauge to an open location. Also check whether the container was already wet or contained water before the measurement period began.
The reading seems too low
A nearby tree, fence, building, or overhanging branch may be blocking rain. Wind can also blow drops away from the opening. Check that the container is level and that the opening is not partly covered by leaves or debris.
The scale is hard to read
Use larger tape labels, place the ruler on the outside of a straight section, or transfer the water carefully into a graduated measuring cylinder with adult help. Pouring can cause water loss, so the direct reading is usually preferable.
Insects or leaves are inside
Empty and rinse the container. Move it away from branches and standing vegetation. Do not add chemicals, soap, or oil to stop insects, because these substances can contaminate the water and change the experiment.
What the Gauge Can and Cannot Tell You
The gauge measures the depth of water collected at one small location. It does not measure the total amount of water in a storm, the size of raindrops, wind speed, or how quickly rain fell. A 10-millimeter reading means that, if the rain had spread evenly over a flat surface, it would form a layer 10 millimeters deep. It does not mean that 10 millimeters fell everywhere in your town.
Your result may differ from an official weather station because of location, container shape, wind, reading time, and equipment quality. Treat the project as a local observation. If you compare your results with an official report, record the station’s distance and measurement period.
Extend the Investigation
Once the gauge is working, use your records to ask new questions:
- Which day had the most rainfall?
- How many rain-free days occurred in a row?
- Does rainfall differ between two safe, open locations?
- Is the monthly total higher or lower than the previous month?
- Do puddles disappear faster after a small rain or a heavy rain?
Make a bar graph with dates along the horizontal axis and rainfall in millimeters along the vertical axis. Label missing or overflowed measurements clearly. At the end of the project, clean the container, dry it, and store it indoors so the plastic, scale, and notebook are ready for the next round of weather observations.