1 - Introduction ~5 mins
Welcome
A bar chart shows which item costs the most. A pie chart answers a different question: what share of the whole does each category take? Today you will decide when a pie is the right tool, roll item costs into category totals, build a pie with percentages, and drop it into {{code:06_ka2_charts}} beside the bar chart you already made.
By the end of this lesson, you will be able to:
- Judge when a pie chart is appropriate for parts of a whole
- Build a pie chart from category totals with percentages
- Sort slice order and avoid too many slices or invalid data
- Add a category cost breakdown pie chart to your charts workbook
Warm-up
Look at your Something Real budget in your head. If you split every euro into categories (materials, travel, promo, kit), which category would take the biggest slice of the pie? That is the story a pie chart is built to tell.
2 - Key Concepts ~6 mins
Read this table before you build. The rules here stop most pie-chart disasters before they start.
| Concept | Why it matters | Example |
|---|---|---|
| Pie chart — a circle divided into slices that show each part as a share of one whole (100%) | Readers see proportions in one glance: "materials take nearly half the budget" is clearer as a slice than as a list of numbers | A Centra stocktake pie: chilled 40%, ambient 35%, bakery 25% of weekly waste euro |
| Parts of a whole — every slice must belong to the same total, and slices should add to about 100% | If the numbers are not parts of one total, the pie lies. Separate totals need a bar chart, not a pie | Cost by Category on one project budget = good pie. Comparing two different months side by side = use bars instead |
| Category totals first — aggregate item rows into a short summary table before you chart | Twenty tiny slices are unreadable. Five category totals make a clean story | Ingredients €85, Packaging €28, Equipment €45, Marketing €20, Transport €12 → five slices, not eight item lines |
| Percentages on slices — labels that show each slice as a % of the total | People misjudge angles. A percentage removes the guesswork when you pitch or hand the chart to a supervisor | Marketing 11% next to the slice — no need to squint at the legend |
| When not to use a pie — too many slices (more than about 6), negative values, or values that are not parts of one whole | A crowded or invalid pie confuses the reader and weakens your KA2 evidence | — |
Worked example: Aoife's market stall budget
Aoife sells custom cupcakes at a weekend market (a small enterprise pitch). Her budget still lives as item rows. A pie of every line would be unreadable, so she first groups by category and adds the costs.
Step A — item list (what she starts with):
| Category | Item | Cost (€) |
|---|---|---|
| Ingredients | Flour and sugar | 40 |
| Ingredients | Butter and eggs | 30 |
| Ingredients | Toppings | 15 |
| Packaging | Boxes | 18 |
| Packaging | Labels | 10 |
| Equipment | Mixer hire | 45 |
| Marketing | Flyers | 20 |
| Transport | Van fuel | 12 |
Step B — roll up each category (add the matching rows):
- Ingredients: 40 + 30 + 15 = 85
- Packaging: 18 + 10 = 28
- Equipment: 45 = 45
- Marketing: 20 = 20
- Transport: 12 = 12
Step C — Category Totals table (what the pie actually charts):
| Category | Total (€) |
|---|---|
| Ingredients | 85 |
| Packaging | 28 |
| Equipment | 45 |
| Marketing | 20 |
| Transport | 12 |
Five slices, one whole (€190), percentages on each slice, largest slice first. In the step-by-step you will type the item list, build this summary the same way, then insert the pie. Independent Practice uses the same group-and-add method on your Something Real budget.
3 - Step-by-step Task ~15 mins
Build Aoife's category pie chart in a sample area of your charts workbook (or a scratch sheet). You will type a short item list, roll the costs into a Category Totals table, insert a pie chart, add percentage labels, set a clear title, and check slice order. Use the same group-and-add steps on your own project in Independent Practice.
4 - Common Issues ~4 mins
Common Issues
| Issue | Solution |
|---|---|
| My pie has dozens of tiny slices and looks unreadable | You charted item rows instead of category totals. Build a short Category / Total table (about 3–6 rows) by grouping items and adding each category, select only that table, and insert the pie again |
| The chart shows the wrong numbers or includes a blank slice | Re-select only the summary range with headings (no empty rows, no Total row that double-counts, and not the longer item list). Delete the old chart and insert a new one from the clean range |
| I cannot find percentage labels | Excel Online: select the chart → turn on Data Labels → choose Percentage. Google Sheets: Chart editor → Customise → Pie chart → Slice label → Percentage |
| One value is negative or the pie looks broken | Pie charts cannot honestly show negative parts of a whole. Fix the data (costs should be positive) or use a bar chart instead |
| I do not know how to get category totals from my own budget | Scan your item list for the same category name, add those costs on paper or in a spare cell, then type one total per category in a two-column summary (same method as Aoife: 40+30+15 = 85 for Ingredients) |
5 - Independent Practice ~20 mins
Independent Practice
- A Category Totals summary (about 3–6 real categories rolled up from your Something Real item costs) sits in the workbook
- A pie chart shows those category shares of one whole, with percentage labels visible on or beside the slices
- The chart has a short factual title and is saved in {{code:06_ka2_charts}} next to your earlier bar chart
- No overcrowded mess: if a category is tiny noise, fold it into "Other" or drop it so the main story stays clear
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