Recipe Scaling

Double a banana bread recipe and convert imperial to metric — with two lines of frontmatter.

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You have an American banana bread recipe written in cups, ounces, and fahrenheit. You need to double the batch for a party, and your kitchen has metric measuring tools. Two lines of YAML frontmatter handle both transformations — every ingredient is scaled and converted automatically.

The complete CalcMark file is available at testdata/examples/recipe-scaling.cm.

Frontmatter: Scale and Convert #

The scale directive multiplies quantities by a factor. Adding Currency to unit_categories makes costs scale too. Custom scales units like bananas and eggs that aren’t in the standard unit library. The convert_to directive converts results to a target measurement system (si or imperial). Together, they transform the entire document.

---
scale:
  factor: 2
  unit_categories: [Mass, Volume, Currency, Custom]
convert_to: si
---

scale: {factor: 2, unit_categories: [Mass, Volume, Currency, Custom]} doubles all quantities, currency values, and custom units. convert_to: si converts imperial units (cups, ounces, fahrenheit) to metric (ml, grams, celsius). You write the recipe once in its original units — the frontmatter does the rest.

CalcMark features: scale frontmatter directive with unit_categories; convert_to frontmatter directive; Currency and Custom opt-in for scaling.

Ingredients #

Write each ingredient as a quantity with its original unit. The displayed results are already doubled and in metric.

flour = 1.5 cups
sugar = 0.75 cups
butter = 4 ounces
milk = 0.25 cups
bananas = 3 bananas
eggs = 2 eggs
baking_soda = 1 teaspoons
salt = 0.25 teaspoons
vanilla = 1 teaspoons

flour is written as 1.5 cups but displays as 720 ml — that’s 1.5 × 2 = 3 cups, converted to milliliters. butter goes from 4 ounces to 227 g. Custom units like bananas and eggs are scaled (3 → 6, 2 → 4) because Custom is in unit_categories, but they aren’t converted since they have no metric equivalent.

CalcMark features: Quantities with units (cups, ounces, teaspoons); custom units (bananas, eggs); automatic scaling; automatic unit conversion.

Oven Temperature #

Temperature is not listed in unit_categories, so it converts but does not scale. Doubling a recipe does not mean doubling the oven temperature — you control this by choosing which categories to include.

oven = 350 fahrenheit

350 fahrenheit converts to 176.666667 celsius. The scale factor only applies to categories listed in unit_categories, so temperature is unaffected.

CalcMark features: Temperature conversion (fahrenheit to celsius); category-based scaling control.

Cost per Loaf #

Because Currency is listed in unit_categories, costs scale with the batch. The @scale directive references the scale factor directly in expressions, so per_loaf stays correct when you change the batch size.

cost_flour = $0.50
cost_sugar = $0.30
cost_butter = $1.50
cost_milk = $0.25
cost_bananas = $0.75
cost_eggs = $0.60

total_cost = cost_flour + cost_sugar + cost_butter + cost_milk + cost_bananas + cost_eggs
per_loaf = total_cost / @scale

Each ingredient cost is doubled by the scale factor. total_cost sums to $7.80 (the doubled batch cost), and per_loaf = total_cost / @scale gives $3.90 — the cost for one loaf. The @scale reference reads the factor from frontmatter, so changing factor: 2 to factor: 5 automatically updates both the scaled costs and the per-loaf calculation.

CalcMark features: Currency literals ($); currency opt-in scaling via unit_categories: [Currency]; @scale directive reference.

What the Frontmatter Does #

Every category is opt-in. To change the batch size, edit scale. To switch between metric and imperial, change convert_to to si or imperial. The rest of the document adjusts automatically.

Features Demonstrated #

This example showcases the following CalcMark features:

• scale frontmatter — doubles every quantity with one line of YAML
• unit_categories filtering — opt-in scaling for Mass, Volume, Currency, Custom
• Custom category — scales custom units like bananas and eggs
• @scale directive — reference the scale factor in expressions
• convert_to frontmatter — converts imperial to metric across the document
• Category-based control — temperature converts but does not scale (not in unit_categories)
• Custom units — bananas and eggs scale without conversion
• Quantities with units — cups, ounces, teaspoons, fahrenheit
• Currency arithmetic — $ preserved through addition and division
• Template interpolation — {{variable}} to embed computed values in prose

Try It #

cm testdata/examples/recipe-scaling.cm