Castile Soap Dilution Calculator

Castile soap is concentrated, so measure before you dilute

Liquid castile soap, the vegetable-oil soap sold by brands such as Dr. Bronner's, is sold as a concentrate and meant to be diluted. The Dr. Bronner's dilutions cheat sheet lists these working dilutions: about 1/4 cup per quart of water for an all-purpose spray, 1 tablespoon per quart for windows, about 1 part soap to 10 parts water for dishes, about 1 part to 3 parts for foaming hand soap, and roughly 1/2 cup in 3 gallons of hot water for mopping. This calculator scales those to any batch and returns tablespoons, cups and mL.

Castile soap is a true soap, not a synthetic detergent, and that shapes what it can and cannot do. It reacts with acids: mixing it with vinegar or lemon juice causes it to curdle into a whitish, greasy residue and cancels the cleaning power of both. Rinse a surface between products instead of combining them in one bottle. This is one of the most common DIY cleaner mistakes.

Soap also reacts with the minerals in hard water and leaves a chalky film or spots, especially on dark surfaces and glass. Distilled water reduces that, and Dr. Bronner's notes that hard water may require hand-drying dishes to prevent spots. Foaming hand soap works only in a pump designed for foam, and the diluted mix has no preservative, so keep batches small and use them within a couple of weeks.

Castile soap cleans by lifting grease and dirt. It is not registered as a disinfectant, so choose a registered product where killing germs matters. Concentrated soap can sting eyes, so rinse right away if it splashes. Do not use it with bleach or ammonia, avoid strong mixes on unsealed wood, and label spray bottles clearly so no one mistakes them for something else. A drop of soap in the wrong bottle, such as a glass spray, is enough to cause streaks, so keep separate bottles for each recipe.

Where these numbers come from

The formulas and default values in this calculator are based on:

• Dr. Bronner's, Dilutions Cheat Sheet for Dr. Bronner's Pure-Castile Magic Soap (all-purpose, window, dish, foaming hand soap and mop dilutions
• hard-water and pre-diluted shelf-life notes)
• Lisa Bronner, Why Vinegar & Castile Soap Don't Mix Well (acid breaks soap into a curdled residue)
• US EPA, What's the difference between products that disinfect, sanitize, and clean surfaces? Note: window and floor ratios are converted from the published per-quart and per-gallon amounts
• confirm on your bottle

This is general household-cleaning guidance and planning math, not medical or professional advice. Product formulas change, so the label on your bottle always wins: follow its directions and warnings, test a hidden spot first, and never mix cleaning products. For a poisoning emergency call Poison Help at 1-800-222-1222 (US), or 911 if someone has trouble breathing.