Converting Sourdough Recipes Between Mass and Volume

Many great sourdough recipes (especially older or family ones) are written in cups and spoons. Modern sourdough is much easier in grams. Here's how to convert reliably.

Why volume measurements are unreliable

A cup of flour can weigh anywhere from 110g to 160g depending on:

• How packed the flour is
• The flour's moisture content
• The flour's protein content
• How you measured (scoop vs. spoon-level)

That's a 30%+ variation. For sourdough where hydration is exact, this is too much.

Standard volume-to-weight conversions

These are the conversions most US recipe writers assume:

Flour

• 1 cup all-purpose flour = 120g
• 1 cup bread flour = 130g
• 1 cup whole wheat flour = 120g
• 1 cup rye flour = 100g
• 1 cup cake flour = 110g

Liquids

• 1 cup water = 240g (240ml)
• 1 cup milk = 240g
• 1 cup oil = 220g (slightly less dense than water)

Salt

• 1 tsp table salt = 6g
• 1 tsp kosher salt (Diamond Crystal) = 3g
• 1 tsp kosher salt (Morton) = 5g
• 1 tbsp = 3 tsp

Other common ingredients

• 1 cup sugar = 200g
• 1 cup brown sugar (packed) = 220g
• 1 stick butter (½ cup) = 113g
• 1 large egg (without shell) = 50g

Converting a typical recipe

Old recipe:

• 4 cups all-purpose flour
• 1.5 cups water
• 1 cup starter
• 2 tsp salt

Converted:

• 480g all-purpose flour (4 × 120)
• 360g water (1.5 × 240)
• 240g starter (1 × 240, assuming 100% hydration starter)
• 12g salt (2 × 6)

Now you have a metric recipe to work with.

Calculating hydration in baker's percentages

Once you have weights, calculate baker's percentages:

• Flour weight = 100% (the base)
• Water weight ÷ flour weight × 100 = water percentage
• Other ingredients: same calculation

For the converted recipe above:

• Flour: 480g (100%)
• Water in dough: 360g
• Water in starter: 120g (assuming 100% hydration starter)
• Total water: 480g (100% hydration!)
• Flour in starter: 120g
• Total flour: 600g
• Recalculate: 480 / 600 = 80% hydration

That's high. Many old recipes call for very wet doughs without saying so.

Sample converted recipe (full process)

Old grandmother recipe:

"4 cups flour, 2 cups warm water, 1 cup starter, 2 tsp salt. Mix and let rise overnight."

Converted:

• 480g flour
• 480g water (2 × 240)
• 240g starter
• 12g salt

Calculate:

• Total flour: 480 + 120 (from starter) = 600g
• Total water: 480 + 120 = 600g
• Hydration: 100% (very wet — basically a no-knead style dough)

Now you can adjust:

• For 80% hydration: reduce water to 360g
• For 75% hydration: reduce water to 330g

You've converted the recipe AND identified its style (very high hydration, no-knead style).

When to trust the original recipe

If grandma's recipe always produced great bread, the percentages probably worked. Convert as written and try it.

If you don't know whether the recipe is reliable, calculate the percentages first. If they're way out of normal ranges (200% hydration, 50% starter), the recipe needs adjustment.

Normal sourdough percentages

For reference:

• Hydration: 65–85% (anything over 90% is unusual)
• Starter: 15–25% (anything over 30% is fast-fermenting)
• Salt: 1.8–2.2% (anything outside 1.5–2.5% is unusual)
• Sugar: 0–10% (in enriched doughs)
• Butter: 0–40% (40% is true brioche)
• Eggs: 0–25% (in enriched doughs)

If your converted recipe is way outside these ranges, double-check your math.

Converting metric to volume (the reverse)

If you need to share a metric recipe with someone using cups, you can convert backward — but the result will be less precise.

To convert grams back to cups, use the same conversion factors:

• 360g flour ÷ 120 = 3 cups flour
• 250g water ÷ 240 = 1 cup water + about 2 tbsp

Mark all conversions as approximate.

A common conversion error

The starter in many old recipes is "1 cup." This is ambiguous:

• Is it 100% hydration starter (240g)?
• Is it stiff starter (50% hydration, packed = 200g)?
• How recently was it fed?

If you're converting an old family recipe, ask the original baker how they maintain their starter. The hydration of the starter affects the math significantly.

If you can't ask, assume 100% hydration starter (240g for 1 cup).

Sourdough scale precision

For sourdough, you want a scale with:

• 1g resolution
• 5kg capacity
• Tare function

A scale with 0.1g resolution is overkill for most sourdough but useful for very precise yeast measurements.

Most home digital scales work fine. A $20 scale lasts years.

Tools that help

• Sourdough calculator — many websites offer ones that calculate baker's percentages from your weights
• Notes app — store your converted recipes for future reference
• Kitchen scale with units — toggle between grams and ounces if needed (use grams)

Common conversions I keep handy

For quick reference:

• 1 cup AP flour = 120g
• 1 cup bread flour = 130g
• 1 cup whole wheat = 120g
• 1 cup water = 240g
• 1 tsp Diamond Crystal kosher salt = 3g
• 1 tsp table salt = 6g
• 1 tbsp olive oil = 14g
• 1 stick butter = 113g
• 1 large egg = 50g

If you bake regularly, these become memorized.

When the math is wrong

Sometimes conversions don't add up to a workable recipe. Reasons:

• The original recipe was inconsistent (different cup measurements throughout)
• The original baker used a non-standard cup size
• The original recipe was a memory, not a written record

In these cases:

• Use the percentages as a guide
• Adjust to typical sourdough ranges
• Test bake and refine

You may end up with a different recipe than the original — but a working one.

A weekend conversion project

If you have a stack of old family recipes, spend a Saturday converting them:

• Calculate percentages
• Identify each recipe's style (high hydration country loaf, enriched sandwich loaf, etc.)
• Test bake your favorites
• Save in a personal recipe book in metric

You'll preserve family bread while making it reproducible.

The benefit of metric

Once you've converted:

• Recipes are reproducible (same result every time)
• Scaling is easy (multiply or divide all weights)
• Comparing recipes is easy (percentages reveal styles)
• You can troubleshoot (you know what your dough actually contains)

Metric isn't just precision. It's understanding what you're baking.