Washing Soda for Laundry: What It Does and How to Use It
LaundroMaps Team
Washing soda is sodium carbonate, an alkaline powder that softens hard water so your detergent can work better (American Cleaning Institute). Add ½ cup with your usual detergent for a regular load, or 1 cup for a large, heavily soiled load or hard water (ARM & HAMMER). It boosts detergent rather than replacing it, and it should stay away from wool and silk (UGA Extension).
Key takeaways
- Use 1/2 cup of washing soda with your normal detergent for a regular load, and 1 cup for large, heavily soiled loads or hard water.
- It softens water by precipitating calcium and magnesium, so it helps most where the water is hard.
- Washing soda is a fairly strong alkali and baking soda is a mild one, so wear gloves with washing soda and keep it out of your eyes.
- Skip it on wool and silk, which need a neutral soap with no free alkali, and on aluminum.
- Washing soda, baking soda and borax are three different compounds, and none of them replaces detergent.
What is washing soda, and what does it do in a wash?
Washing soda is a grainy white powder of sodium carbonate and water (ARM & HAMMER). The American Cleaning Institute (ACI) describes sodium carbonate as a fairly strong alkaline salt that supplies cleaning power and softens water by precipitating the hardness minerals out of solution (American Cleaning Institute). Retail washing soda is the hydrated crystalline form, and soda ash is the name for the anhydrous (water-free) form (American Cleaning Institute; ARM & HAMMER).
In a wash it does three jobs (American Cleaning Institute):
- Softens water: it is a precipitating builder, a material that makes detergent work better by disabling hardness minerals.
- Raises alkalinity: that helps loosen acidic soils and keeps the wash water at an effective level.
- Helps with greasy soils: builders emulsify oily soils and keep removed soil from settling back onto fabric.
It does not replace detergent. ARM & HAMMER, which makes a washing soda, calls it a booster that supplements your detergent's stain-fighting power (ARM & HAMMER).
Is washing soda good for laundry?
It is good for laundry in hard water and for heavily soiled loads. The U.S. Geological Survey says hard water is high in dissolved calcium and magnesium, soap reacts with the calcium to form soap scum, and more soap or detergent is needed to get laundry clean (USGS). USGS also says hard water can shorten the life of fabrics and clothes (USGS).
The USGS scale puts hard water at 121 to 180 mg/L as calcium carbonate and very hard water above 180 mg/L (USGS). In those ranges, a booster that ties up the minerals makes sense. If your water is soft, there is little for washing soda to soften.
Laundromat machines run on the local water supply, so a self-service laundromat in a hard-water area gives the same hard water you would have at home. Check the posted machine rules first, and add the powder where the machine allows.
How much washing soda do you use per load?
ARM & HAMMER's directions for its washing soda cover these situations (ARM & HAMMER):
| Situation | Amount | How |
|---|---|---|
| Regular load | ½ cup | Add with your usual liquid or powder detergent at the start of the wash |
| Large, heavily soiled load | 1 cup | Same, at the start of the cycle |
| Hard water | 1 cup | Treat it like a large, heavily soiled load |
| HE washer | ½ cup | Put it in the HE dispenser with the detergent |
For set-in stains, the same maker gives a pretreat and a soak (ARM & HAMMER):
- Pretreat: mix 4 tablespoons of washing soda with ¼ cup of warm water into a paste, rub it gently into the dampened stain with rubber gloves, then wash.
- Soak: use 2 tablespoons per gallon of warm water in a tub, or ½ cup in a filled washer, for at least 30 minutes.
- Test first: check a small hidden area for colorfastness, and use cool water for colorfast items when soaking.
These are the maker's directions for its own product. Follow the machine's instructions for adding laundry products.
Washing soda vs baking soda: which is better for laundry?
Are they the same thing?
No. Washing soda is sodium carbonate, and baking soda is sodium bicarbonate (ARM & HAMMER). ACI calls sodium carbonate a fairly strong alkali and sodium bicarbonate a mild alkali (American Cleaning Institute). Washing soda does not contain baking soda (ARM & HAMMER).
Which should you pick?
Pick washing soda for hard water and greasy or heavily soiled loads, where its stronger alkalinity and water softening help (American Cleaning Institute). Pick baking soda for mild odor and everyday boosting. ARM & HAMMER says its baking soda neutralizes odors by balancing pH and softens wash water, and it directs ½ cup in the washer plus another ½ cup in the rinse (ARM & HAMMER). Our baking soda in laundry guide covers that in full.
Washing soda vs borax: what is the difference?
Washing soda is sodium carbonate, and borax is sodium borate (American Cleaning Institute). 20 Mule Team, which makes borax, says washing soda has a pH of 11 and that borax is also quite alkaline, though not to the same level (20 Mule Team Borax). ACI calls borax mildly alkaline: it buffers alkalinity, helps loosen soils and stains, and in diaper presoaks it inhibits ammonia odors (American Cleaning Institute). Both soften water (20 Mule Team Borax).
| Washing soda | Baking soda | Borax | |
|---|---|---|---|
| Compound | Sodium carbonate | Sodium bicarbonate | Sodium borate |
| Strength | Fairly strong alkali | Mild alkali | Mildly alkaline |
| Main job | Softens water, boosts cleaning | Odor, gentle boost | Buffers, loosens soil |
| Maker's regular-load amount | ½ cup | ½ cup | ½ cup |
The strength and job rows come from ACI's glossary (American Cleaning Institute). The amounts come from each maker's own directions (ARM & HAMMER; ARM & HAMMER; 20 Mule Team Borax).
Is washing soda just borax?
No. They are different compounds, and borax carries its own safety rules. Poison Control notes that borax is not banned in the U.S., but the EPA classifies it as a moderate acute toxicity substance that can cause harm in higher doses, especially if ingested or if it gets in the eyes (Poison Control). Keep either powder away from children and pets.
Is washing soda the same as OxiClean?
No. OxiClean's maker lists the key ingredient of its formulation as sodium percarbonate, alongside sodium carbonate, surfactants and polymer (OxiClean). Sodium carbonate, the whole of a washing soda, is one ingredient in that stain remover. Washing soda alone contains no sodium percarbonate.
What are the disadvantages of washing soda, and what should you not use it on?
Its alkalinity is the drawback. Wool is sensitive to alkaline agents, and UGA Extension says washable wool and silk need a neutral soap with no free alkali (UGA Extension). Keep washing soda out of loads with those fibers and read the care label first (see our silk washing guide).
Handle it with care (ARM & HAMMER):
- Gloves: avoid contact with eyes and prolonged skin contact, and wear gloves.
- Skin: rinse well with water.
- Eyes: flush thoroughly with water.
- Swallowed: rinse the mouth, drink a full glass of water, contact a physician, and do not induce vomiting.
- Aluminum: do not use it on aluminum pots, pans or surfaces.
For any ingestion in the US, call Poison Control at 1-800-222-1222 (Poison Control).
Can you make your own washing soda?
ARM & HAMMER notes that baking soda can be used to make a DIY washing soda (ARM & HAMMER). We did not find a tested home method from an extension service or agency, so this guide gives no oven temperatures or times. Store-bought washing soda is sodium carbonate and water (ARM & HAMMER), and it comes with directions.
Frequently asked questions
Can I use just washing soda for laundry?
No. Washing soda softens water and boosts cleaning, but ARM & HAMMER describes it as a booster that supplements your detergent. Use it with your usual detergent.
Why is washing soda rarely used for washing clothes?
It is a strong alkali that wool and silk cannot tolerate, and it helps most when water is hard or loads are heavily soiled. Many people get what they need from detergent alone.
Is washing soda safe for a washing machine?
Used as directed, yes: ARM & HAMMER lists amounts for regular and HE washers. Skip it on aluminum surfaces and keep the powder out of eyes.
What is the difference between washing soda and soda ash?
Soda ash is the anhydrous, water-free form of sodium carbonate. Washing soda is the hydrated crystalline form sold at retail.
How we researched this
We read the American Cleaning Institute's glossary, USGS's water hardness page, UGA Extension's fiber guide, Poison Control, and the laundry directions of the makers of washing soda, baking soda, borax and OxiClean, all on 13 October 2026. Maker instructions are used only for each maker's own product. We did not lab-test any method, and we did not find a verified home method for making washing soda, so we left it out.
Sources
- American Cleaning Institute -- Glossary of Cleaning Product Terminology
- ARM & HAMMER -- How to Use Super Washing Soda
- University of Georgia Extension -- Understand Your Fibers
- U.S. Geological Survey -- Hardness of Water
- ARM & HAMMER -- How to Get Laundry Extra Clean and Fresh with Baking Soda
- 20 Mule Team Borax -- Borax vs Washing Soda
- 20 Mule Team Borax -- Borax laundry directions
- Poison Control (National Capital Poison Center) -- Borates, borax, and boric acid: Are they safe?
- OxiClean -- How Does OxiClean Work? Ingredients
Related guides
- Borax for laundry: what it does, how much to use and how safe it is.
- Homemade laundry detergent: how washing soda fits into a DIY mix.
