Can You Mix 20 and 40 Developer to Make 30? 30 + 40 and 20 + 30 Too
Yes, on paper. Equal parts of two developer volumes land halfway between them: 20 + 40 vol works out at about 9% (the strength sold as 30 vol), 20 + 30 at about 7.5% and 30 + 40 at about 10.5%, neither of them a strength the ranges quoted here sell as a bottle. The sums assume both bottles hold their labelled strength and are measured accurately. No published test in the sources checked for this article compares a blend with a factory bottle, so if the formula calls for 30 vol, use a 30 vol bottle.
Can you mix different developer volumes?
Yes, on paper. For any pair, multiply each strength by its parts (measured the same way the label is), add them, and divide by the total parts, taking 10, 20, 30 and 40 vol as about 3, 6, 9 and 12% hydrogen peroxide. Equal parts 20 + 40: (6 + 12) ÷ 2 = 9%, the strength sold as 30 vol. A blend always lands between its two bottles, never above the stronger one. The last column follows each blend into a Life Color Plus bowl at the standard 1:1.5 (50 ml colour to 75 ml developer), where the colour dilutes it again.
| Blend (parts) | Works out at about | A factory strength? | Bowl at 1:1.5, starting peroxide |
|---|---|---|---|
| 20 vol + 40 vol, equal parts | 9% (30 vol) | Yes, sold as 30 vol | 5.4% |
| 30 vol + 40 vol, equal parts | 10.5% (roughly 35 vol, not a sold label) | No | 6.3% |
| 20 vol + 30 vol, equal parts | 7.5% (roughly 25 vol, not a sold label) | No | 4.5% |
| 10 vol + 30 vol, equal parts | 6% (20 vol) | Yes, sold as 20 vol | 3.6% |
| 10 vol + 20 vol, equal parts | 4.5% | Not a permanent-colour developer strength in the ranges quoted; nowhere near 30 vol | 2.7% |
| 40 vol + 10 vol, equal parts | 7.5% (roughly 25 vol, not a sold label) | No | 4.5% |
| 1 part 40 vol + 2 parts 10 vol | 6% (20 vol) | Yes, sold as 20 vol | 3.6% |
| 2 parts 40 vol + 1 part 10 vol | 9% (30 vol) | Yes, sold as 30 vol | 5.4% |
Peroxide arithmetic only. Factory 20, 30 and 40 vol at 1:1.5 start the bowl at about 3.6%, 5.4% and 7.2%. Both peroxide columns treat millilitres as equal weights (no developer density is given in the sources checked); the bowl column also assumes a peroxide-free colour cream and describes the moment of mixing. The "roughly 25/35 vol" labels are arithmetic on the 3%-per-10-vol convention; no range quoted here sells them. "Factory strength" means one listed for the permanent colour ranges quoted here; none of their makers gives guidance on blending two strengths of its own developer.
Can you mix 20 and 40 developer to make 30?
Yes, in peroxide terms: equal parts of 20 vol (6%) and 40 vol (12%) give about 9%, which is 30 vol. "40 and 20" is the same blend; pouring order doesn't change the sum. Mixed 1:1.5 with Life Color Plus, the bowl starts at about 5.4% peroxide on paper, the same starting figure a factory 30 vol gives at that ratio. Whether it then processes the same has not been tested.
The catch is accuracy. The bottles are 6 points apart, so errors count. In a 75 ml developer portion, pouring about 4 ml too much 40 vol (41 ml of 40 to 34 ml of 20) moves the blend from 9% to about 9.3%. That is about a tenth of the 3-point step between two factory strengths, before the colour dilutes it to about 5.6% instead of 5.4% in the bowl.
Shelf strength is the larger unknown. No source checked for this article measures how much cream developer loses on the shelf; plain pharmacy peroxide solutions in one study (abstract only) stayed at or above 90% of label over its study period. If the 40 vol were at that 90% floor, an equal-parts blend with a true 20 vol would land at about 8.4%, not 9% (about 28 vol), and start a Life Color Plus bowl at about 5.0% instead of 5.4%. And with core Majirel, a 20 + 40 blend puts a 40 vol bottle into a range L'Oréal caps at 30 vol, even though the blend sits at 9%.
Can you mix 30 and 40 developer?
Yes, on paper: equal parts of 30 vol (9%) and 40 vol (12%) give about 10.5%, a strength none of the developer ranges quoted here is sold at. On the 3%-per-10-vol convention that is roughly 35 vol, a label no range quoted here uses. In a Life Color Plus bowl at 1:1.5 it starts at about 6.3%, between a factory 30 vol (5.4%) and 40 vol (7.2%).
That in-between strength is the problem. FarmaVita, Wella, Schwarzkopf and L'Oréal each name bottled strengths, and none of their documents quoted here names a halfway point or says what 10.5% does with its colour. For scale: Wella's UK Koleston Perfect sheet puts the two bottles one level of lift apart for its own colour (9% "2 levels", 12% "3 levels"), so a 30 + 40 blend is chasing a half-level no maker quoted here documents. With core Majirel it is also above the 9% maximum on L'Oréal's global page. If 30 vol won't give the lift a formula needs, go back to the colour's own instructions rather than splitting the difference; for Life Color Plus, see the developer decision guide and the high-lift series.
The 3-point gap halves the measuring error: the same 4 ml slip moves the blend about 0.15 of a point, a twentieth of a factory step.
Can I mix 20 and 30 developer together?
Yes, on paper: equal parts of 20 vol (6%) and 30 vol (9%) give about 7.5% (roughly 25 vol on the same convention), halfway between, and not a strength any range quoted here sells. So mixing them simply gives you something weaker than 30 and stronger than 20: at 1:1.5 with Life Color Plus the bowl starts at about 4.5%, against 3.6% from 20 vol and 5.4% from 30 vol.
None of the colour instructions quoted here names 7.5%, so there is no published result to plan around. If the choice is between 20 and 30, decide on the job (white coverage or lift) rather than splitting the difference; the developer decision guide sets out which strength does which job.
Can you mix 30 and 10 developer to make 20?
Yes, on paper: equal parts of 10 vol (3%) and 30 vol (9%) work out at about 6%, which is 20 vol. At 1:1.5 the bowl starts at about 3.6% peroxide on paper, the same starting figure a factory 20 vol gives at that ratio. As with 20 + 40, the 6-point gap makes measuring errors count.
Not every line sells a 10 vol bottle. Wella's UK Koleston Perfect fact sheet lists Welloxon Perfect at 4%, 6%, 9% and 12%, while Wella's US store lists 1.9%, 3%, 6%, 9% and 12%; Schwarzkopf's IGORA ROYAL Technical Manual (GB edition) includes "3% 10 Vol.", and FarmaVita lists 10 vol (3%). If your line makes a 20 vol, that bottle removes the measuring error and the mixing of two formulations.
Why a blend is less predictable than a bottle
The labels are approximate. 3, 6, 9 and 12% is a trade convention, not an exact conversion: the European Pharmacopoeia says its own 3% solution "corresponds to about 10 times its volume of oxygen", and allows it to run from 2.5% to 3.5% by weight.
True to label is an assumption. No published measurement in the sources checked shows how much strength cream developer loses on the shelf or after opening. The nearest evidence is on plain pharmacy peroxide solutions: a stability study (abstract only) reported they stayed at or above 90% of labelled content over its study period, and called storage in light "inadmissible"; it gives no loss rates. Wella's US Welloxon Perfect page says to keep developer away from heat and light, in a cool place.
A developer is a formulation, not just a percentage. Henkel's developer patent describes an oil-in-water cream with added peroxide stabilisers, buffered to pH 3–5. That is a patent example, not the formula of any bottle on sale, and no source says whether two strengths from one brand share a base, or what happens when two bases are combined. Watering a strong developer down works for the peroxide sum, but dilutes the acid buffer and stabiliser with it.
Makers name bottles, not blends. Wella's Welloxon Perfect is "TO BE USED IN COMBINATION WITH WELLA PROFESSIONALS HAIR COLOR AND LIGHTENERS", and L'Oréal's global Majirel page says "Use exclusively with L'Oréal Professionnel Oxydant 12.5, 20 and 30 volume (3.75%, 6% and 9%) maximum". Neither addresses blending. If you blend at all, blend toward a strength your colour's own instructions name.
What this means for a Life Color Plus bowl
Life Color Plus has a factory bottle at every strength its directions call for, so there is no need to blend. FarmaVita lists its Life cream developer at 2.5, 5, 10, 20, 30 and 40 vol (0.75 to 12%); this site carries 10, 20, 30 and 40 vol, and the colour directions call for 20, 30 or 40.
FarmaVita's directions give 50 ml of colour plus "75 ml of Cream Developer at 20 – 30 – 40 volumes" (1:1.5), a 1:1 option "to obtain a stronger colour", and 100 ml at 40 vol "in case of super-bleaching products" (1:2; see the high-lift series). The ratio is the second lever: 30 vol starts at about 5.4% at 1:1.5 and 4.5% at 1:1; 40 vol at 1:2 at about 8%. More in Life Color Plus mixing ratios in practice.
Quick answers
Can you mix 10 and 20 developer to make 30?
No. A blend always lands between its two bottles, so 10 vol (3%) and 20 vol (6%) give somewhere from 3% to 6%, never 9%. Reaching 30 vol needs at least one bottle at 30 vol or stronger.
How do you dilute 40 or 30 volume developer to 20 (or 40 to 30)?
On paper, with 10 vol: equal parts 30 + 10, or one part 40 to two parts 10, both work out at about 6%; two parts 40 to one part 10 gives about 9% (30 vol). Water lowers the peroxide too, but thins the buffer and stabiliser, and no source tests that. The predictable route is the factory bottle.
Can you mix developers from different brands, or pre-mix a blend?
Wella ties Welloxon to Wella colour and L'Oréal ties Majirel to its own Oxydant (quoted above), so a blend of either with another brand is outside that maker's stated use; see can you mix developers across brands. No source covers how a pre-blended developer keeps; Wella's instruction to use a colour mixture immediately and discard the rest covers colour plus developer, not two developers.
Which is stronger, 30 or 40 developer?
40 vol: about 12% hydrogen peroxide against 9%. In GB and the EU, 12% is also the most a hair product may contain once ready for use (Annex III of Regulation 1223/2009), so 40 vol sits at that ceiling; US industry data report a 50 vol (15%) professional developer that is diluted as needed. Wella's UK Koleston Perfect sheet gives 9% at 1:1 "2 levels of lift" and 12% "3 levels of lift": Wella's claim for its own colour, not a rule for other brands.
Will 30 volume developer lighten hair by itself?
It isn't made to. Two developer patents describe developer as acidic (Henkel pH 3–5, Clairol pH 2–6), and Clairol's puts the alkaliser in the colour. Peroxide needs alkaline conditions to form the perhydroxyl anion, believed to be an important oxidant of melanin: worked out from peroxide's published pKa, about 0.0002% is in that form at pH 6 against about 2% at pH 10, roughly ten thousand times apart, though the anion may not be the only species involved. That is mechanism, not measurement: no published study measures lightening on hair from developer alone at developer pH, and no maker of a current commercial developer publishes its pH. Manufacturers state lift only for the mixed system, and Wella's page says: "DO NOT APPLY THIS PRODUCT DIRECTLY TO THE HAIR". For the low end of the ladder, see 1.9% developer explained.
How long should you leave 40 volume developer on?
In Wella and Schwarzkopf's charts the time is printed per colour range, with one time covering every strength in it: Koleston Perfect prints one "30-40 mins without heat" panel for 4% to 12% at 1:1, and IGORA ROYAL "30–45 minutes" for its 3/6/9% and 12% ranges alike. That doesn't mean strength never matters: in L'Oréal's Majirel, 40 vol appears only in the 50-minute High Lift row. With bleach, the blend sum is the same, but timing and strength belong to the lightener's own instructions. For Life Color Plus, work to the timing in the instructions supplied with the colour.
Colour chemistry: questions colourists ask.
See also: Can You Mix Developers Across Brands? · 1.9% developer explained · Mixing Permanent and Demi Colour in the Same Bowl
Shades: Life Color Plus tubes, £3.49
Sourced to the European Pharmacopoeia hydrogen peroxide monographs; Annex III of Regulation (EC) 1223/2009 as retained in GB law and the EU consolidated text; the Cosmetic Ingredient Review Final Report on Hydrogen Peroxide (2018); Wella's Koleston Perfect UK fact sheet and Welloxon Perfect product pages; Schwarzkopf Professional's IGORA ROYAL Technical Manual (GB edition); L'Oréal Professionnel's Majirel US usage sheet and global Majirel page; FarmaVita's Life Color Plus directions and developer listing; patents from Henkel (US 4,927,627 / EP 0 308 825) and Clairol (CA 2129491); and peer-reviewed work by Smith et al. (2017), Wolfram et al. (1970) and Madanska et al. (2004). Always work to the instructions supplied with the product you are using.
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