Mass: Grams and Kilograms

Overview

Lesson 3 of 7 in Measuring Tools and Units. Students investigate mass using balance and digital scales, choosing appropriate units, recording measurements and comparing classroom objects.

Learning intentions

• WALT measure, compare and estimate mass in grams and kilograms.
• WALT select an appropriate unit and measuring tool.
• WALT explain and record measurements accurately.
• WALT use mathematical language to compare and order masses.

Success criteria

• I can choose grams or kilograms appropriately.
• I can use a balance scale or digital scale correctly.
• I can record a mass with the correct unit.
• I can compare and order masses from lightest to heaviest.

Curriculum links

• Measurement: estimate, measure and compare mass using grams and kilograms.
• Number: use place value and the relationship between kilograms and grams, including 1 kilogram = 1,000 grams.
• Mathematical communication: explain measurement choices and justify whether estimates are reasonable.
• Key competencies: thinking; participating and contributing; managing self.

Lesson structure (30 minutes)

1. 0–4 minutes – Hook and prior knowledge

Open with the opening question and mass images: “Which is heavier: a classroom book or a packet of paper? How could we find out?” Show a small object and a larger object, inviting students to make a silent estimate before discussing with a partner.

Establish that mass describes how much matter an object has. Clarify that everyday speech often says “weight”, but in this lesson we are measuring mass in grams and kilograms.

2. 4–9 minutes – Teach units and tools

Use the grams-and-kilograms teaching slides to introduce the relationship 1 kg = 1,000 g. Discuss sensible choices: a paperclip is measured in grams, while a school bag is more suitable for kilograms.

Model a pan balance: place the object in one pan and known masses in the other, keeping the scale steady. Then model a digital scale: reset or tare it, place the object in the centre, wait for the reading and check the unit. Read the scale slowly, pointing to colour-coded intervals.

3. 9–12 minutes – Estimate and compare

Give each pair two visible objects, such as a pencil case and a book. Students use the lighter/heavier icons on the estimate-and-compare prompt to predict which has greater mass and choose grams or kilograms for each.

Invite two pairs to explain their choices. Emphasise that an estimate should be close enough to be sensible, not an exact answer.

4. 12–22 minutes – Pair investigation

Arrange 10 pairs. Each pair receives two or three classroom objects and a balance or digital scale. Distribute the mass investigation sheet. Students estimate each object, select a unit, measure it, record the mass and unit, then order their objects from lightest to heaviest.

Encourage students to handle scales carefully and check that digital scales show zero before measuring. Pairs may share recording duties: one student measures and reads, while the other records and then swaps roles.

If equipment is limited, pairs rotate through a measurement station while others complete estimates and comparisons. The teacher circulates, asking: “Why did you choose grams?” and “How do you know this object is heavier?”

5. 22–27 minutes – Discuss and extend

Use the investigation discussion slides to display three sample masses. Students compare them using words such as lighter than, heavier than, equal to and approximately.

Challenge students who finish early to convert a measured mass in kilograms to grams, calculate the total mass of two objects, or explain whether an estimate was reasonable. For example: “A bag is estimated at 2 kg but measures 350 g. Is the estimate reasonable? Explain.”

6. 27–30 minutes – Plenary and check

Return to the success criteria and exit prompt. Students tell a partner one object best measured in grams and one best measured in kilograms, explaining why.

Collect the investigation sheets or hear selected responses. Revisit any common error, such as writing “250” without a unit or confusing the heavier object with the larger-looking object.

Resources

• the complete mass lesson slide deck, including the hook, teaching sequence, activity instructions, discussion prompts and plenary.
• the mass investigation sheet for estimates, measurements, units and ordering.
• Pan balances and standard masses, where available.
• Digital scales, with spare batteries if needed.
• Ten sets of safe classroom objects with varied masses.
• Grams/kilograms reference cards.
• Lighter/heavier icons and coloured labels for scale intervals.
• Board or modelling table for recording examples.

Assessment

• Observe whether students select a suitable unit, tare or balance the scale correctly, and read the measurement accurately.
• Check investigation sheets for an estimate, measured mass, correct unit and ordered objects.
• Listen for explanations using comparative language and the relationship between kilograms and grams.

Differentiation

• Begin with concrete objects and labelled scales. Model each step slowly, including zeroing the digital scale and reading intervals.
• Provide a grams/kilograms reference card, colour-coded scale intervals, a visual word bank and lighter/heavier icons. Accept spoken explanations instead of written explanations where appropriate.
• Pair students strategically and allow collaborative recording. For dyslexic learners, use a clear sans-serif font, short instructions, generous spacing and uncluttered worksheet sections.
• Support students who need more structure with two familiar objects and whole-number readings. Extend confident learners with kilogram-to-gram conversions, combined masses and reasonableness explanations.