Class 7 · Science and environment
Make a rain gauge and record rainfall
The weather report says "15 mm of rain fell". What does that mean, and could you measure it yourself?
What you will learn: Build a simple rain gauge and record rainfall in millimetres over time.
Small test at the end: scroll down to the end of this page for five short questions that check what you have learnt. Tap an answer, then press Check answer. Go to the questions ↓
Jump to: Check yourself · For grown-ups · For teachers
Safety first
Gauge on the ground. Never climb. Empty it every day. Stay in during storms.
Keep it safe:
- A grown-up does any cutting of bottles and smooths sharp edges.
- Put the gauge on open ground. Never climb on a roof, wall or tree to place it.
- Do not go out in storms or lightning to read it; read it after.
- Empty it every day so mosquitoes cannot breed in standing water.
You will need
- A clear, straight-sided jar or bottleSame width all the way up. A grown-up can cut the top off a straight plastic bottle.
- A ruler and tapeTape the ruler on the outside with 0 at the inside bottom.
- A notebookFor your daily log.
- StonesTo keep the jar steady.
Time: Long project: 2 weeks.
The story
The radio says, "15 mm of rain fell last night." Tanmay looks at the puddle outside the stall. "That puddle is much deeper than 15 mm!" Tara wonders what the number really measures. Could they catch the rain themselves, and measure it?
The idea
Rainfall is measured as the depth of water that falls, in millimetres (mm).
A rain gauge is a straight-sided container left in the open. If the water inside is 12 mm deep, 12 mm of rain fell.
The sides must be straight (the same width from top to bottom), or the depth would not match the rain that fell.
Place it in the open, away from roofs and trees that could drip into it or block it. Read and empty it at the same time each day.
Worked example
Arjun's rainfall week
- His gauge: a straight-sided jar with a ruler taped to the outside, 0 at the bottom of the water.
- Each morning at 8 am he read the depth and emptied the jar.
- Week: 3, 0, 12, 5, 0, 8, 2 mm.
- Total: 3 + 0 + 12 + 5 + 0 + 8 + 2 = 30 mm.
Wednesday was wettest with 12 mm; the whole week had 30 mm.
Try it
Make the gauge.
Tape the ruler to the outside of the jar so 0 lines up with the inside bottom.
Place it.
On open ground, away from roofs and trees, with stones around it to keep it upright.
Read it daily.
At the same time each day, read the depth at eye level and write the date and mm.
Empty it.
Pour the water onto a plant and put the gauge back.
Graph it.
After a week or two, draw a bar graph of mm for each day and find the total.
What you make (paper or offline)
Your rainfall log
A log with dates, times and mm.
A bar graph with labelled axes.
The total and the wettest day.
Make it on paper. Keep it with you. Nothing to upload.
Check yourself
Five questions about what this page teaches. Choose an answer and press Check answer, or open "See the answer and why". Nothing is saved or sent: your choices stay on this screen and disappear when you leave or reload the page.
How do you want to answer? You choose, and you can change at any time.
See the answer and why
- A. 12 mm Correct. In a straight-sided gauge, the depth of water is the rainfall.
- B. 1.2 mm Not this one. That divides by 10. The depth is the rainfall.
- C. It depends on how wide the jar is Not this one. In a straight-sided jar, the width does not change the depth of rain.
- D. 120 mm Not this one. That multiplies by 10. The depth is the rainfall.
See the answer and why
- A. So that birds cannot drink the water from it Not this one. That is not the reason. Accurate depth is.
- B. So it looks neat in the garden Not this one. Looks do not matter. Accurate depth does.
- C. So the depth inside matches the rain that fell Correct. A jar that widens or narrows would make the depth too small or too big.
- D. So it holds more water Not this one. The amount is not the point. Accurate depth is.
See the answer and why
- A. Because rain does not fall near trees Not this one. Rain falls there too. Trees just change what reaches the gauge.
- B. Roofs and trees make the rain fall much faster there Not this one. They do not change how fast rain falls.
- C. They can drip extra water in or block the rain Correct. Then the gauge would not measure the rain that fell in the open.
- D. So nobody can find it Not this one. It should be easy to reach safely.
See the answer and why
- A. 30 mm Correct. 3 + 0 + 12 + 5 + 0 + 8 + 2 = 30.
- B. 12 mm Not this one. 12 mm is the wettest day, not the total.
- C. 7 mm Not this one. 7 is the number of days.
- D. 28 mm Not this one. Add again: the total is 30.
See the answer and why
- A. Because the ruler gets wet Not this one. The ruler is on the outside. That is not the reason.
- B. So each reading is one day's rain, and mosquitoes cannot breed Correct. Daily emptying gives daily readings and stops standing water.
- C. Because water goes bad in one hour Not this one. Water does not go bad that fast. Daily readings and mosquitoes are the reasons.
- D. To make the total look bigger Not this one. Emptying does not change the real rainfall.
Think back
Which day had the most rain?
Did your total match the weather report? Why might it be different?
Investigate further
- Compare your readings with a friend's gauge in a different place.
- Keep a log for a whole month of the monsoon.
- Kabir's gauge under the roof edge read 2 cm, Tara's in the open read 1 cm, after the same rain. Did more rain fall at Kabir's spot? (No: water running off the roof added to his gauge. Gauges go in the open, away from roofs and trees.)
Same spark, other subjects
Water in a tub
What floats, what sinks, what mixes, and why towns grow beside rivers.
- Floated or sank? Sort and count Science · Class 1
- Why the Lemon Floats and the Potato Sinks Physics · Class 5 · Learning guide
- Separating Mixtures Chemistry · Topic ladder, Classes 8–10
- Big Cities Sit by Water... So Why Is Delhi Big? Geography and history · Class 5 · Learning guide
- How much does a dripping tap waste? Maths · Class 4
For grown-upsTap a heading to open it. The safety notes are at the top of the page.
Before you start
- Cut a straight plastic bottle if needed and smooth the edge. Choose a safe, open spot on the ground.
Questions that help
- "Is your eye level with the water when you read it?"
- "Why the same time each day?"
What's really going on
Weather stations use the same idea, with standard gauges. Small home gauges can differ from reports because rain varies from place to place.
Emptying daily is important: standing water is a mosquito breeding site.
Other ways to do it
- In the dry season, measure water from a watering can sprinkled over the gauge and a flat tray to see that depth is the same in both.
For teachersLearning aims, classroom ideas and what to look for.
Learning aims
- Construct a simple rain gauge and record rainfall in mm.
- Present a time series as a bar graph and total it.
Subject links
- Science: weather and measurement.
- Geography: rainfall and climate.
- Mathematics: data and addition.
These links are general. They have not been checked against a specific board syllabus.
In the classroom
- Place two or three gauges around the school and compare readings.
What to look for
- Straight-sided gauge, zeroed ruler, daily reading at the same time.
- Correct total and labelled graph.