Hair dye guide
Running out of dye mid-application is one of the most stressful things that can happen during a DIY color session. It leaves you with patchy, uneven results that are hard to fix. This guide tells you exactly how many boxes to buy for every combination of hair length and thickness — so you never run short.
If you have medium-thickness hair and just want a fast answer, use this table. If your hair is fine or thick, scroll down for the adjusted numbers.
| Hair length | Examples | Boxes needed (medium hair) |
|---|---|---|
| Pixie cut | Under 2 inches | 1 box |
| Short | 2–4 inches, ear-length | 1 box |
| Bob | Chin to shoulder | 1–2 boxes |
| Medium / long | Below shoulder | 2 boxes |
| Very long | Mid-back to waist | 3 boxes |
| Extremely long | Hip-length and below | 3–4 boxes |
Always buy one extra box
Most stores — including Walmart, Target, and Sally Beauty — accept returns on unopened, unused boxes of hair dye. Buy one more than you think you need. Running short mid-application is a much bigger problem than having a spare box.
Hair thickness (also called density) is the biggest variable most people overlook. Two people with identical waist-length hair can need very different amounts of dye — because one person has a small, fine ponytail while the other has a thick, coarse one.
The rule of thumb: fine hair needs about 25% less product than medium hair, and thick or coarse hair needs 40–50% more.
| Length + thickness | Boxes needed | Notes |
|---|---|---|
| Short + fine | 1 box | May only use half — save the rest as a strand test |
| Short + thick | 1–2 boxes | Buy 2 if your ponytail is wider than a quarter |
| Bob + fine | 1 box | Fine bobs absorb product quickly — apply fast |
| Bob + medium | 1–2 boxes | Buy 2 to be safe |
| Bob + thick | 2 boxes | Definitely 2 — thick bobs surprise people |
| Long + fine | 1–2 boxes | 1 box often works but have a backup ready |
| Long + medium | 2 boxes | Standard recommendation |
| Long + thick | 3 boxes | Most common reason people run short |
| Very long + fine | 2 boxes | 2 is usually enough for fine waist-length hair |
| Very long + medium | 3 boxes | Standard for waist-length medium hair |
| Very long + thick | 3–4 boxes | Do not underestimate this combination |
Yes — significantly. Curly and coily hair is more porous than straight hair, meaning it absorbs more product per strand. Curly hair also has more surface area due to its spiral shape, even when the same length as straight hair.
If your hair is curly or coily, add approximately 25% more dye on top of the thickness-adjusted amount. So if thick straight long hair needs 3 boxes, thick curly long hair may need closer to 3.5 — meaning you should buy 4.
The number of boxes stays roughly the same whether you're going lighter or darker, because the amount needed is determined by your hair volume — not the color direction. However, if you're going lighter, you'll likely need bleach kits in addition to your dye boxes. Bleach is a separate product from hair dye and follows the same length/thickness rules.
Going darker is easier than going lighter
Permanent hair dye deposits color into the hair shaft. Going darker works more predictably because you're adding pigment. Going lighter with dye alone only works 1–2 shades lighter on virgin (never-colored) hair. Anything more requires bleach first.
Check our bleach & developer calculator if you're planning to lighten significantly.
Root touch-ups use significantly less product than full-color applications because you're only covering the regrowth area — typically 1–2 inches at the roots. For most hair lengths and thicknesses, a single box is enough for a root touch-up. The exception is very thick, very long hair where the regrowth band may be large enough to need 2 boxes.
Mix all your boxes in a bowl before starting. If you're using multiple boxes of the same shade, combining them ensures a consistent mixture rather than working from separate batches. A good visual check: the mixed dye should coat the bottom of the bowl with at least a 1-inch depth for short hair, 2 inches for medium hair, and 3+ inches for long or thick hair.
Want an exact number based on your specific hair length, thickness, texture, and target color?
Use the free hair dye calculator →Waist-length thick hair is the most demanding combination — you'll need 3 to 4 boxes. Buy 4 to be safe. The large surface area combined with thick hair density means a single or double box will almost certainly leave you short, resulting in patchy roots or faded ends.
It depends on thickness. For fine to medium shoulder-length hair, 1 box is usually enough. For thick shoulder-length hair, you'll likely need 1.5 to 2 boxes. Always have a second box available — even if you don't open it, the peace of mind is worth it.
You can mix two permanent shades from the same brand and product line in equal parts to get a blended result. Do not mix permanent with demi-permanent dye, and always follow with a strand test before doing a full application. Our color mixing calculator shows you the exact ratios and developer amounts.
This is the scenario everyone wants to avoid. If you run out mid-application, cover your hair with a plastic cap immediately to slow processing, then rush to buy another box. The color may be slightly uneven where the application was interrupted, but catching it within 20–30 minutes is usually manageable. The bigger problem is matching the exact shade on a second trip — always buy enough the first time.