DIY Laundry Soap: A 3-Ingredient Recipe That Makes 5 Gallons

• Give A Shit About Nature
• April 12, 2026
• Sustainable Living
• 0 Comments

Have you noticed that store-bought laundry detergent has gotten expensive? A mid-range bottle runs $15 or more, it comes in single-use plastic, and most of it is water you’re paying to ship. The recipe below costs a fraction of that, makes five gallons at a time, and has exactly three ingredients. It’s been in regular use in this household for over a decade.

Let’s get into it.

What you’ll need

Ingredients:

• ½ bar (2.5 oz) Fels-Naptha bar soap, grated
• 1 cup washing soda (not baking soda — they’re different)
• 1 cup borax

Equipment:

• 5-gallon bucket with lid
• Cheese grater or food processor
• Large pot
• Long stirring spoon
• Whisk or handheld mixer (for later)

Optional: 20–30 drops of essential oil if you prefer a scented detergent. Lavender and lemon are common choices. Skipping it leaves clothes smelling clean and neutral, which is the preference here.

Instructions

1. Grate the soap. Use a standard cheese grater to grate half of a Fels-Naptha bar. A food processor works too if you want to move faster. You’re just trying to get it into small pieces that will melt quickly and evenly.

2. Heat a half gallon of water. Bring it to hot but not boiling — around 160–180°F. Add your grated soap and stir until fully melted. Don’t rush this with high heat; you just want it dissolved, not scorched.

3. Fill your bucket. Add 4.5 gallons of hot tap water to your 5-gallon bucket. Stir in the washing soda and borax until both are fully dissolved.

4. Combine. Pour the melted soap mixture into the bucket. Stir thoroughly to combine everything.

5. Let it sit. Over the next several hours, the detergent will thicken as it cools. Left completely undisturbed overnight, it can set into a firm gel. This is normal and not a problem. Before your first use, break it up with a whisk or handheld mixer until it reaches a pourable consistency.

Tip for a runnier detergent: Adding an extra half gallon of water (making 5.5 gallons total) produces a looser, less gel-prone consistency that’s easier to pour without sacrificing cleaning performance. Worth trying if you find the standard batch too thick.

How to use it

Use about ¼ cup per load in a standard washing machine. High-efficiency (HE) machines need less — start with 2 tablespoons and adjust from there. HE machines use less water and are sensitive to excess suds, so err on the low side until you know what works for your machine.

This detergent is low-sudsing by nature, which is part of why it works in HE machines at all. If you’re used to seeing a lot of bubbles as a sign that soap is “working,” this will look different — but suds aren’t what cleans your clothes.

Storage and shelf life

Store in your 5-gallon bucket with the lid on. The detergent will continue to settle between uses, so give it a stir or shake before each use — or keep a long-handled spoon nearby. At a household of three, a full batch typically lasts five to seven months.

There’s no expiration date to worry about with this formula. The ingredients are stable indefinitely. If the gel gets too thick over time, add a little warm water and stir.

The cost breakdown

Prices vary by region and retailer, but as a general reference:

• Fels-Naptha bar soap: around $2 per bar (you use half)
• Washing soda (55 oz box): around $5–6, yields many batches
• Borax (76 oz box): around $6–7, also yields many batches

A single 5-gallon batch costs roughly $2–3 in materials. At ¼ cup per load, 5 gallons provides approximately 80 loads. That works out to about 2–4 cents per load, compared to 20–35 cents per load for most commercial detergents.

Common questions

Does DIY laundry soap actually clean clothes well? Yes, for most household laundry. Fels-Naptha is a surfactant-based bar soap with a long history as a laundry pre-treater and cleaner. Washing soda is a strong alkaline cleaner that boosts stain removal and softens water. Borax adds cleaning power and helps neutralize odors. For heavily soiled work clothes or athletic wear, pre-treating stains with undiluted Fels-Naptha before washing improves results.

Is borax safe? Borax (sodium tetraborate) is a naturally occurring mineral compound and has been used in laundry products for over a century. It’s an irritant in its dry powder form — avoid inhaling it and keep it away from children and pets during mixing. Once dissolved in a large volume of water, residual concentrations in your wash are very low. If you prefer to avoid it entirely, some people substitute an extra cup of washing soda, though this reduces cleaning performance somewhat.

Will this work in an HE washing machine? Yes, in smaller quantities. Use 2 tablespoons rather than ¼ cup, and choose the cold or warm water cycle. The low-sudsing formula is compatible with HE machines, but using too much in a low-water machine can leave residue on clothes.

Why washing soda and not baking soda? They’re chemically similar but not interchangeable. Baking soda is sodium bicarbonate; washing soda is sodium carbonate. Washing soda is significantly more alkaline, which makes it a more effective cleaning agent and water softener for laundry purposes. You can make washing soda from baking soda by spreading it on a baking sheet and heating it at 400°F for about an hour — though buying it directly is easier and inexpensive.

Can I use a different bar soap? Fels-Naptha is the most commonly used because it’s formulated specifically for laundry and available at most grocery and hardware stores. Zote and Kirk’s Castile are popular alternatives. Ivory soap also works. Avoid heavily moisturizing soaps — the added oils can leave residue on fabrics over time.

Does it work in cold water? Yes, though hot water dissolves the soap more effectively during the making of the detergent. Once mixed, the formula works in cold, warm, or hot wash cycles.

Is this detergent safe for septic systems? Generally yes. Borax and washing soda are both considered septic-safe at these concentrations. If you have concerns specific to your system, consult your septic service provider.

Where to find the ingredients

All three ingredients are available at most grocery stores, hardware stores, and big-box retailers in the laundry aisle. Fels-Naptha, washing soda (look for Arm & Hammer Super Washing Soda), and borax (20 Mule Team is the most widely available brand) are often sold together.

One more thing

Five gallons is a lot of detergent. It’s also the entire point. Making a big batch means you’re not back at the store in three weeks, you’re not going through another plastic jug, and you’ve got enough on hand that laundry stops being a thing you need to think about for months at a time.

Scale the recipe up or down as needed — it’s proportional — but if you have the storage space, the full batch is worth it.