Converting Percentages to Weight
Simple math for accurate formulation at any batch size
Formulas Are Written in Percentages
Professional cosmetic formulas list ingredients as percentages of the total batch. This makes formulas universal - they work at any batch size. To actually make the product, you need to convert those percentages to weight (grams or wt oz) for your specific batch size.
Grams vs Weighted Ounces
Both grams (g) and weighted ounces (wt oz) are accurate weight measurements. Use whichever your scale displays! Avoid fluid ounces (fl oz) - those measure volume, not weight. 1 wt oz = 28.35g
The Basic Concept
Percentage means "per hundred." So 5% means 5 parts per 100 parts. If your batch is 100 grams, 5% = 5 grams. If your batch is 16 wt oz, 5% = 0.8 wt oz. The calculation is just simple multiplication.
Why Percentages?
- Universal: Same formula works for 50g test batch or 5kg production
- Shareable: Anyone can reproduce your formula at their preferred size
- Industry standard: All suppliers list usage rates as percentages
- Safety verification: Easy to check if ingredients are within safe limits
The Conversion Formula
One simple formula handles all conversions:
Weight = (Percentage ÷ 100) × Batch Size
or equivalently
Weight = Percentage × (Batch Size ÷ 100)
Works for grams OR weighted ounces!
Breaking It Down
Example: 5% preservative in a 200g batch
- Step 1: Convert percentage to decimal: 5 ÷ 100 = 0.05
- Step 2: Multiply by batch size: 0.05 × 200 = 10g
- Result: You need 10g of preservative
Same example in wt oz: 5% preservative in a 16 wt oz batch
- Step 1: Convert percentage to decimal: 5 ÷ 100 = 0.05
- Step 2: Multiply by batch size: 0.05 × 16 = 0.8 wt oz
- Result: You need 0.8 wt oz of preservative
The Shortcut for Easy Batch Sizes
This is why many formulators start with 100g test batches:
For 100g batches: Percentage = Grams
5% = 5g, 10% = 10g, 0.5% = 0.5g - no calculation needed!
For 16 wt oz (1 lb) batches: Percentage (as a decimal) × 16 = wt oz
5% = 5 ÷ 100 = 0.05 × 16 = 0.8 wt oz, 10% = 10 ÷ 100 = 0.1 × 16 = 1.6 wt oz, 25% = 25 ÷ 100 = 0.25 × 16 = 4 wt oz
Quick Reference Multipliers
Gram Batches:
| Batch Size | Multiply % By |
|---|---|
| 50g | 0.5 |
| 100g | 1 (just use the %) |
| 200g | 2 |
| 500g | 5 |
| 1000g (1kg) | 10 |
Ounce Batches:
| Batch Size | Multiply % By |
|---|---|
| 8 wt oz | 8 |
| 16 wt oz (1 lb) | 16 |
| 32 wt oz (2 lbs) | 32 |
| 48 wt oz (3 lbs) | 48 |
| 64 wt oz (4 lbs) | 64 |
Convert % to decimal first (÷ 100), then multiply by batch oz
Worked Examples
Practice with real formulation scenarios
Example 1: Simple Lotion (100g / 3.5 wt oz batch)
| Ingredient | % | Grams | Wt Oz |
|---|---|---|---|
| Water | 68% | 68g | 2.4 oz |
| Glycerin | 5% | 5g | 0.18 oz |
| Emulsifying Wax | 5% | 5g | 0.18 oz |
| Sweet Almond Oil | 20% | 20g | 0.7 oz |
| Preservative | 1% | 1g | 0.04 oz |
| Fragrance | 1% | 1g | 0.04 oz |
| Total | 100% | 100g | 3.5 oz |
Example 2: Same Lotion Scaled to 16 wt oz (1 lb)
Convert each percentage to a decimal (÷ 100), then multiply by 16:
| Ingredient | % | Calculation | Wt Oz |
|---|---|---|---|
| Water | 68% | 0.68 × 16 | 10.88 oz |
| Glycerin | 5% | 0.05 × 16 | 0.8 oz |
| Emulsifying Wax | 5% | 0.05 × 16 | 0.8 oz |
| Sweet Almond Oil | 20% | 0.20 × 16 | 3.2 oz |
| Preservative | 1% | 0.01 × 16 | 0.16 oz |
| Fragrance | 1% | 0.01 × 16 | 0.16 oz |
| Total | 100% | 16 oz |
Example 3: Body Butter (500g / 32 wt oz batch)
| Ingredient | % | Grams | Wt Oz |
|---|---|---|---|
| Shea Butter | 50% | 250g | 16 oz |
| Mango Butter | 20% | 100g | 6.4 oz |
| Coconut Oil | 15% | 75g | 4.8 oz |
| Jojoba Oil | 12% | 60g | 3.84 oz |
| Vitamin E | 1% | 5g | 0.32 oz |
| Fragrance | 2% | 10g | 0.64 oz |
| Total | 100% | 500g | 32 oz |
Scaling Up and Down
The beauty of percentage-based formulas is easy scaling. Here's how to calculate any batch size.
Method 1: Direct Calculation
For each ingredient: (Percentage ÷ 100) × Batch Size = Weight
Example: 8% ingredient in a 350g batch
(8 ÷ 100) × 350 = 0.08 × 350 = 28g
Same in ounces: 8% ingredient in a 24 wt oz batch
(8 ÷ 100) × 24 = 0.08 × 24 = 1.92 wt oz
Method 2: Multiplier Method
Calculate your multiplier once, then use it for all ingredients:
Grams: Multiplier = Batch Size ÷ 100
Wt Oz: Multiplier = Batch Size ÷ 100 (same formula!)
- • 350g batch: 350 ÷ 100 = 3.5 multiplier → 8% = 28g
- • 24 wt oz batch: 24 ÷ 100 = 0.24 multiplier → 8% = 1.92 wt oz
Method 3: Ratio Scaling
If you already have weights for one batch size, scale to another:
New Weight = Old Weight × (New Batch ÷ Old Batch)
Example: Scale a 16 wt oz recipe to 48 wt oz:
- • Scale factor: 48 ÷ 16 = 3
- • If you had 2.4 wt oz of oil, now you need: 2.4 × 3 = 7.2 wt oz
Scaling Tip
Always double-check that your final weights add up to your intended batch size. Rounding errors can accumulate. If they don't match, adjust your largest ingredient (usually water) to make up the difference.
Tips & Common Questions
Dealing with Small Percentages
Some ingredients are used at very small percentages (0.1% - 1%). For accuracy:
- Use a 0.01g (or 0.001 wt oz) precision scale for small amounts
- Make larger batches so small percentages become measurable weights
- A 0.5% ingredient in a 100g batch = 0.5g (hard to measure)
- A 0.5% ingredient in a 500g batch = 2.5g (easier to measure)
What If My Percentages Don't Add to 100%?
All cosmetic formulas should total exactly 100%. If they don't:
- Over 100%: You have an error - recheck your math
- Under 100%: Add the difference to your main ingredient (usually water in lotions, or base oil in anhydrous products)
Converting Drops to Weight
"Drops" aren't a reliable measurement (they vary by dropper, viscosity, and technique). To convert:
- • Essential oils: ~20-25 drops per gram (~600 drops per wt oz)
- • Thin liquids: ~30-35 drops per gram
- • Better approach: Always weigh, don't count drops
Use a Spreadsheet
Create a simple spreadsheet with your formula percentages in one column and a formula to calculate weights based on your batch size. Change the batch size cell, and all amounts update automatically. This eliminates calculation errors.
Practice Problems
Test your understanding with these exercises
Problem 1
A formula calls for 3% emulsifier. How much do you need for a 16 wt oz batch?
Show Answer
(3 ÷ 100) × 16 = 0.03 × 16 = 0.48 wt oz
Problem 2
You need 0.8% preservative in a 300g batch. How many grams?
Show Answer
(0.8 ÷ 100) × 300 = 0.008 × 300 = 2.4g
Problem 3
Your lip balm formula is: 35% beeswax, 35% coconut oil, 28% sweet almond oil, 2% flavor oil. Calculate weights for a 8 wt oz batch.
Show Answer
Multiplier: 8 ÷ 100 = 0.08
- • Beeswax: 35 × 0.08 = 2.8 wt oz
- • Coconut Oil: 35 × 0.08 = 2.8 wt oz
- • Sweet Almond Oil: 28 × 0.08 = 2.24 wt oz
- • Flavor Oil: 2 × 0.08 = 0.16 wt oz
- • Total: 8 wt oz ✓