Use 99% isopropyl alcohol when you need a solvent that evaporates fast and leaves virtually no water behind. That covers electronics, flux, adhesive residue and surface prep. Use a 70% mix when you want the alcohol to stay wet on the surface longer, which covers most everyday hard-surface cleaning. Stronger isn't always better. CDC's guidance on alcohol puts its most effective range at 60–90% in water, not 99%.
You don't need to stock every strength, either. One container of 99% makes all of them. The chart and mixing steps are below.
What the percentage on the label means
The number is alcohol by volume. A 70% solution has 70 parts isopropyl alcohol in every 100 parts of finished mix, and the rest is water. A 99% solution is nearly pure alcohol with about 1% water.
The water isn't filler. It changes how the alcohol behaves. More water means slower evaporation and more working time on the surface. Less water means faster flash-off and less risk to anything that doesn't like moisture.
Isopropyl alcohol strengths compared
| Strength | How it behaves | Good for | Not ideal for |
|---|---|---|---|
| 99% | Flashes off in seconds, near-zero residue | Circuit boards and flux, thermal paste, adhesive residue, surface prep, resin 3D prints | Jobs where the surface needs to stay wet |
| 80–90% | Still fast, with a little more working time | Ink, marker and sticky residue when 99% dries before you finish wiping | Circuit boards (stick with 99%) |
| 70% | Stays wet longer | Everyday hard-surface cleaning, stainless, benchtops | Circuit boards and connectors |
| 50–60% | Gentler, with more working time | Glass, mirrors, stainless, and tape prep (3M specifies a 50/50 IPA and water wipe for its VHB tapes) | Heavy residue |
| 10–20% | Light-duty | Inspection wipes between polishing steps. Most detailers stay around 10–15%. | Degreasing |
Why 70% often works better than 99%
It sounds backwards, since stronger should work better. But CDC's disinfection guidance puts the optimum range for alcohol at 60–90% in water, and it notes that alcohol with no water in it works less well. There are two reasons:
- Water helps. Alcohol works on microbes by denaturing (unfolding) their proteins, and CDC notes that happens faster when water is present.
- Working time. 99% also flashes off faster in practice, so it spends less time wet on the surface. A 70% mix stays wet longer.
One note on labels: what alcohol can do in a lab study and what a product is labeled for aren't the same thing. Industrial IPA is sold as a solvent and cleaner, not as a disinfectant, sanitizer or antiseptic. If a job calls for a registered disinfectant or sanitizer, like a healthcare room or a food-contact surface, use a product that's labeled for that job.
Isopropyl alcohol dilution chart (starting from 99%)
The 90% to 50% ratios are the same ones printed on our label. All of the ratios are rounded to easy numbers and land within a point of the target, which is plenty accurate for cleaning. If you want it exact, measure the IPA from the chart, then fill with water up to the final line.
| Target strength | Easy ratio (IPA : water) | 32 oz spray bottle | 1 gallon | 1 liter |
|---|---|---|---|---|
| 90% | 10 : 1 | 29 oz IPA | 116 oz IPA | 909 mL IPA |
| 80% | 4 : 1 | 26 oz IPA | 103 oz IPA | 808 mL IPA |
| 70% | 7 : 3 | 22.5 oz IPA | 90.5 oz IPA | 707 mL IPA |
| 60% | 3 : 2 | 19.5 oz IPA | 77.5 oz IPA | 606 mL IPA |
| 50% | 1 : 1 | 16 oz IPA | 64.5 oz IPA | 505 mL IPA |
| 25% | 1 : 3 | 8 oz IPA | 32.5 oz IPA | 253 mL IPA |
| 10% | 1 : 9 | 3.25 oz IPA | 13 oz IPA | 101 mL IPA |
In each column, measure the IPA and then add distilled water up to the bottle size. For a gallon of 70%, that's 90.5 oz of IPA with water added to the 128 oz mark.
How to mix it
- Pick your spot. Mix somewhere ventilated and away from flames, pilot lights and sparks.
- Use a clean, compatible container. Standard HDPE and polypropylene spray bottles handle IPA fine. Don't reuse food or drink bottles.
- Measure the IPA first and pour it in.
- Top up with distilled or deionized water to the final line. Tap water leaves mineral spots on glass and electronics.
- Cap it and turn it over a few times to mix.
- Label it with the contents, the strength and the hazard warnings (flammable, causes eye irritation). In a workplace, OSHA's hazard communication rules require labels on containers you fill yourself, unless you're using it up right away.
Why fill to the line instead of adding a set amount of water? Alcohol and water shrink a little when you mix them. 70 oz of IPA plus 30 oz of water gives you slightly less than 100 oz. Measuring the alcohol and then filling to the line keeps the strength where you want it.
The formula for any strength
Say you want a 16 oz bottle of 70% from 99% IPA. That's 16 × 70 ÷ 99 = 11.3 oz of IPA, then water to the 16 oz line.
The same formula works from other strengths. A quart (32 oz) of 70% made from 91% alcohol takes 32 × 70 ÷ 91 = 24.6 oz of the 91%.
Buy 99%, mix what you need
Buying 99% and diluting it yourself stretches every gallon:
| You start with (99%) | Makes this much 70% | Makes this much 50% |
|---|---|---|
| 1 gallon | about 1.4 gallons | about 2 gallons |
| 5-gallon pail | about 7 gallons | about 9.9 gallons |
| 55-gallon drum | about 78 gallons | about 109 gallons |
[PRODUCT: 99% Isopropyl Alcohol, 5-gallon pail and 55-gallon drum. Image, price, link to {{URL_PRODUCT_IPA99}}]
Storing IPA and your mixes
- Keep it capped. 99% IPA pulls moisture out of the air, and it evaporates. An open container doesn't stay 99% for long.
- Diluted doesn't mean non-flammable. 50% and 70% mixes still carry a flammable-liquid rating on their safety data sheets. Treat a spray bottle with the same care as the drum it came from.
- Store it cool and ventilated, away from heat, flame and oxidizers.
- Keep it out of reach of kids, and never store it in anything that looks like a drink.
Frequently asked questions
Is 99% isopropyl alcohol stronger than 70%?
It has more alcohol, but it isn't better at every job. 99% is the better solvent for electronics and residue. 70% is better when you want the alcohol to stay wet on a surface longer.
What percentage of isopropyl alcohol is best for cleaning electronics?
For circuit boards and internals, use 99%, or 90% at minimum. For screens and cases, follow the maker's guidance. Many, including Apple, allow 70% wipes. Power the device off, apply the alcohol to a cloth or swab, and let everything dry completely before you turn it back on.
Which is better for cleaning, 75% or 99% IPA?
It depends on the job. Use 70–75% for hard surfaces where you want more working time. Use 99% for electronics, adhesive residue and surface prep, where you want it gone fast with nothing left behind.
Can you dilute 99% isopropyl alcohol with tap water?
You can, but distilled or deionized water is better. Tap water minerals can leave spots and streaks, especially on glass and electronics.
Is 70% isopropyl alcohol the same as rubbing alcohol?
The strength is the same, but the product isn't. Rubbing alcohol is made and labeled as a first-aid product. Industrial IPA isn't for use on skin at any dilution. Here's how isopropyl alcohol and rubbing alcohol differ. For where each strength gets used, see our guide to isopropyl alcohol uses.
PRO CARE GENIUS
Pure Power. Professional Results.
Questions about IPA or bulk orders? Call 844-GENIUS-0.