Borax vs Washing Soda: Which Is Better for Laundry?

If you have hard water, buy washing soda. If your water is soft and your problem is musty smells, buy borax. That covers most households, and the sections below explain why so you can check it against your own machine and water.

What are borax and washing soda, and are they interchangeable?

Borax and washing soda are not interchangeable: washing soda is sodium carbonate, a strong alkali, while borax is sodium tetraborate, a milder boron mineral salt.

Washing soda has a pH around 11 in solution. It binds the calcium and magnesium that make water hard, and it helps break down greasy soils. Borax sits closer to a pH of 9 to 9.5. It softens water only modestly, but it buffers the wash and is widely used to knock back odors.

Neither is a detergent, because neither has the surfactants that lift and suspend dirt. Either one is a laundry booster that helps your regular detergent do its job.

Borax vs washing soda: side-by-side comparison

In a side-by-side comparison, washing soda wins on water softening and grease, borax wins on gentleness and odor control, and the two tie on price.

Which wins for hard water, soft water, and front-load machines?

Washing soda is the better choice for hard water, and borax or nothing at all is usually enough for soft water.

Water above roughly 120 milligrams per liter (about 7 grains per gallon) is generally classed as hard. In that range, minerals tie up detergent, leave a gray film on whites, and make towels stiff. A scoop of washing soda grabs those minerals before they interfere. If you don't know your hardness, a cheap test strip or your utility's annual water report will tell you. If it's very hard, a whole-house water softener will do more than either powder.

In soft water, washing soda has little left to do except raise alkalinity, and too much alkalinity is rough on fabric. Borax is the gentler pick there.

Front-load and HE washers

A front-load washer uses far less water, so undissolved powder can cling to gaskets and dark clothes. Dissolve your booster in a cup of warm water first, then pour it into the drum rather than the dispenser drawer. Start at the low end of the dose, about one-quarter cup. Pre-dissolving also helps in cold cycles, where both powders dissolve slowly.

How much does each cost per load?

Borax and washing soda both cost roughly 10 to 25 cents per load, so price should not decide this one.

Typical U.S. shelf prices run about $4 to $6 for a 55-ounce box of washing soda and $5 to $8 for a 65-ounce box of borax, though region and retailer move those numbers more than the product does. Store brands, warehouse clubs, and bulk bags usually come in lower.

To work out your own number:

1. Measure your usual dose (say one-quarter cup) onto a kitchen scale and note the ounces. It's often around 2 ounces, but weigh yours.
2. Divide the box weight by that dose. A 55-ounce box at 2 ounces per load gives about 27 loads.
3. Divide the box price by the loads. A $5 box over 27 loads is about 18 cents per load.

Doubling the dose doubles the cost and rarely improves results.

Are they safe for septic systems, sensitive skin, and cloth diapers?

Borax and washing soda are both generally fine for a septic system in normal laundry amounts, but each has skin and handling cautions, and cloth diapers call for care.

Septic systems

Washing soda is a common household alkali and typically causes no trouble in a septic system at laundry doses. Borax in small amounts is generally considered tolerable too, though long-term heavy use is not well documented, and boron can harm plants if your laundry water goes to a graywater system. Graywater rules vary by state and county, so check local code before sending wash water to landscaping. If you're on septic, spread loads through the week and ask your septic pro or local health department about boron limits.

Sensitive skin

Washing soda is the more caustic of the two, so wear gloves when you handle it and run an extra rinse if anyone in the house reacts to residue. Borax can irritate skin and eyes, and it is harmful if swallowed. Keep both in a closed container, high up, away from children and pets. If someone swallows either one, call Poison Control at 1-800-222-1222. The U.S. Consumer Product Safety Commission at cpsc.gov publishes safety information on household chemicals. For detergents with screened ingredients, the EPA Safer Choice label is a good starting point.

Cloth diapers

For cloth diapers in hard water, we'd pick washing soda at a low dose with an extra rinse, because mineral buildup is a common cause of lingering odors and repelling. Borax is a milder choice for soft water. Diaper makers differ on what additives they allow, so check the care tag or the maker's instructions before adding either one.

Can you use washing soda and borax together in laundry?

Yes, you can use washing soda and borax together, and a common approach is one-quarter cup of each in a full load alongside regular detergent.

The combo makes sense in moderately hard water with a smelly load, such as gym clothes or towels. Washing soda softens, borax deodorizes. Start low. If clothes feel stiff or look dull, you're using too much.

The popular homemade detergent recipe (grated bar soap plus equal parts borax and washing soda) is a different thing. Soap-based mixes can leave scum in hard water and cold cycles, and they tend to build up in front-loaders and on cloth diapers. We'd skip it and boost a real detergent instead.

Verdict: which one should you buy?

Buy washing soda if your water is hard or average, and borax if your water is soft or odors are your main problem.

• Hard water or greasy work clothes: washing soda.
• Soft water, musty loads: borax.
• Front-load washer, cold water: either one, pre-dissolved in warm water.
• Septic system: either one in small doses, with loads spread out.
• Cloth diapers: washing soda for hard water, borax for soft, after checking the maker's instructions.
• Sensitive skin or small kids at home: a low dose with an extra rinse and locked-up storage, or neither.

Your next step is simple. Check your water hardness, weigh one scoop of whichever powder you pick, and work out your cost per load before you stock up.