Build a rain gauge and read rain in millimetres

The idea

Rainfall is measured as the depth of water that would cover flat ground, in millimetres, and a wide funnel feeding a narrow tube multiplies that depth so small falls can be read.

What you need

• 1 straight-sided clear plastic container (the reading tube; not glass outdoors)
• 1 funnel wider than the container (measure both diameters)
• ruler in millimetres and a permanent marker
• bricks or a stake to hold the gauge upright in the open, away from walls and trees
• a measuring cylinder to calibrate
• the school's daily 9 am reading time

How to do it

1. Measure the inside diameter of the jar and the mouth diameter of the funnel. Work out both areas (pi x radius squared) and the ratio funnel area divided by jar area: this is the multiplier.
2. Calibrate: pour 10 mL of water into the jar and mark the level; repeat to 50 mL. Convert each mark to millimetres of rain by dividing the depth of water in the jar by the multiplier.
3. Set the gauge in the open, funnel up, level and secured.
4. Every school day at 9 am read the level, record the rainfall in millimetres, empty the jar and reset.
5. Compare the class reading with the Bureau of Meteorology 9 am reading for the nearest station and record both.
6. Graph the month's rainfall as columns and total it.

What you should see

A funnel of 100 cm2 mouth area over a jar of 20 cm2 gives a multiplier of 5, so 1 mm of rain (1 litre per square metre) appears as 5 mm of water in the jar, and a reading of 25 mm in the jar means 5 mm of rain fell. Class readings are compared with the nearest official station; differences come from the distance to that station as well as splash-in, wind and shelter, which the class investigates.

What changes

This activity lists no variables to change, measure and keep the same.

Common misconceptions

Each of these ideas is wrong, and the activity is a chance to test it.

• A wider bucket collects more rain, so it rained more (depth, not volume, is the measure).
• Rainfall is measured in litres.
• A day with no reading means it did not rain (it means no one read the gauge).

Safety card

Curriculum references

The NSW syllabus outcomes and Australian Curriculum v9 codes this activity supports. They are references, not a verified or complete curriculum alignment.

• Science and Technology K-6 Syllabus (2017), current, taught until 2026; skill outcome only: the 2017 syllabus has no Stage 2 content on rainfall or the water cycle (weather data is collected in Stage 1, under ST1-10ES-S); code read from the syllabus document on 22 September 2026ST2-1WS-S
• Science and Technology K-6 Syllabus (2024), implemented from 2027; NESA's timeline is 2026 plan and prepare and 2027 start teaching, and schools may choose to implement it during 2026; code read from the outcomes page on 22 September 2026ST2-DAT-01
• Australian Curriculum v9AC9S4U02AC9S4H01AC9S4I03AC9S4I04

Sources

The pages the author read to write this activity.

1. www.scootle.edu.au/ec/search?accContentId=AC9S4U02
2. curriculum.nsw.edu.au/learning-areas/science/science-and-technology-k-6-2024/outcomes
3. www.nsw.gov.au/education-and-training/nesa/curriculum/science/science-and-technology-k-6-2017
4. primaryconnections.org.au/v84-sequences/water-works
5. primaryconnections.org.au/v84-sequences/weather-my-world