How to Dilute 91% or 99% Isopropyl Alcohol to 70% (Any Bottle Size)

This is pure dilution math. The two things that matter are your starting percentage and your final bottle volume.

10–13 min read Alcohol dilution

Part of the main guide

This article belongs to the Surface Cleaning Guide, where readers can compare alcohol dilution, peroxide mixing, branded cleaner ratios, and other practical surface-cleaning guides.

Quick answer

Use C1V1 = C2V2. If you want a final volume of V2 at 70% from a starting alcohol of C1: V1 (starting alcohol) = (70 ÷ C1) × V2. Then add water: water = V2 − V1. Follow product label instructions and local guidance for intended use.

If you want the calculator to do the math for any bottle size instantly, use the Cleaning Dilution Calculator. Keep alcohol away from flames/heat sources (flammable).

What this is for (and what it’s not)

This guide is for dilution math and safe handling basics. It’s not a promise that a DIY mix meets every disinfection standard for every situation. Always follow product label instructions for contact time, surface suitability, and ventilation.

If you’re mixing anything based on label wording, this helps: How to Read Cleaning Dilution Instructions on Labels.

Quick tables (common bottle sizes)

Diluting 91% to ~70%

Formula: V1 = (70 ÷ 91) × V2. Water is the remainder to reach the final volume.

Final bottle 91% alcohol (V1) Water to add
100 mL ≈ 77 mL ≈ 23 mL
500 mL ≈ 385 mL ≈ 115 mL
1 liter (1000 mL) ≈ 769 mL ≈ 231 mL
32 oz (≈ 946 mL) ≈ 728 mL ≈ 218 mL

Diluting 99% to ~70%

Formula: V1 = (70 ÷ 99) × V2.

Final bottle 99% alcohol (V1) Water to add
100 mL ≈ 71 mL ≈ 29 mL
500 mL ≈ 354 mL ≈ 146 mL
1 liter (1000 mL) ≈ 707 mL ≈ 293 mL
32 oz (≈ 946 mL) ≈ 669 mL ≈ 277 mL

If you want to work in ratios instead of percentages, your ratio explainer helps users: What Does a 1:10 Dilution Mean?

Safety notes that matter (short, practical)

  • Flammable: keep away from flames, heat, and sparks. Ventilate.
  • Don’t mix with bleach: never combine in the same bottle or bucket.
  • Surface check: alcohol can damage some plastics, finishes, and screens—spot test first.
  • Label first: if the product provides specific directions, follow them over internet recipes.

For the “don’t mix” safety cluster: Can You Mix Bleach and Rubbing Alcohol?