How do you convert volume to percentage?

Divide the volume by 10, then multiply by 3. For example, 20 vol / 10 = 2, then 2 x 3 = 6%. So 20 vol = 6% hydrogen peroxide. Alternatively, percentage = volume x 0.3.

How do you convert percentage to volume?

Divide the percentage by 3, then multiply by 10. For example, 9% / 3 = 3, then 3 x 10 = 30 vol. So 9% = 30 vol. Alternatively, volume = percentage / 0.3.

Is 40 volume developer safe to use?

40 vol (12%) is the strongest developer used in salons and should only be used off-scalp (not applied directly to the scalp). It is suitable for high-lift tints and maximum lightening with bleach on resistant hair. Never leave 40 vol on for longer than recommended as it significantly increases the risk of damage and chemical burns.

What does volume mean in developer?

Volume indicates how many times the developer releases its own volume in oxygen gas. 20 vol developer releases 20 times its volume in oxygen. More oxygen means more lightening power. The oxygen opens the cuticle and oxidises the melanin pigment in the hair.

CutCalcs

Peroxide Volume Calculator — Volume & Percentage Converter

Convert between peroxide volumes and percentage strengths and see lift capability for each strength.

Convert From

Developer Volume

Common values: 10, 20, 30, 40

How We Calculate This

This calculator converts between the two measurement systems used for hydrogen peroxide developer: volume (vol) and percentage (%).

Conversion formulas

Percentage = Volume x 0.3

Volume = Percentage / 0.3

Standard equivalents

10 vol = 3%
20 vol = 6%
30 vol = 9%
40 vol = 12%

Frequently Asked Questions

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Last updated: February 2026

All calculations are estimates. Always perform a strand test before chemical services.