Cutting Homemade Soap: Timing, Sizing, and Techniques

Woman slicing a homemade soap loaf with a knife.

So, you’ve spent hours reading all about making soap at home and purchased all of your supplies. Finally, you got the courage to give it a try.

Now, you’re staring at your newly made loaf of soap wondering, “Now what?”

How should homemade soap be cut? Freshly made soap should be sliced in approximately 1 inch bars 24 – 48 hours after pouring. Once the soap has been removed from the mold, a sharp knife or dough scraper will cut it easily. A ruler, miter box, or soap cutting box will help keep the bars evenly sized.

Although it is normal to be a bit nervous when cutting your soap for the first time, the following tips will have you slicing like a pro in no time.

When to Cut Homemade Soap

As soon as the lye solution is added to the oils, the process of saponification begins.

This is really the magic of soap making. The lye molecules bond with those of the oils to form soap and glycerin.

Within 24 hours or so, much, but not all, of the process is complete, and the fluid mixture that you poured into your mold has turned into a solid.

At this point, most soaps will be firm enough to remove from the mold but soft enough to be sliced into bars.

Some soaps won’t reach this point until 48 hours after pouring, and that’s fine. It just means you need to wait an extra day before viewing your creation.

Don’t wait too long though, or the soap will be too hard to cut nicely.

So, how can you tell if your soap is ready to remove from the mold?

A soap that has hardened sufficiently won’t cling to the mold and will keep its shape.

Many soap makers prefer to use silicone soap molds ( I love these things!) because they’re flexible enough that you can gently tug them away from the soap to check for hardness and they release the soap very easily.

Others prefer to use a liner, such as parchment paper or cling wrap, to line a solid mold, and this is okay too.

Just carefully remove the loaf of soap from the mold and gently pull away the liner. If soap is sticking to the liner or it starts to lose its shape, put it back in the mold and give it another 24 hours to harden.

Note that at this stage, there is some unreacted lye still present in the soap, which can burn skin, so be sure to wear gloves. (Be sure to read this for more safety guidelines.)

On a brighter note, soap that has just been unmolded is still fairly soft. If you notice any uneven edges or flaws, now is the time to very gently smooth them out with your fingertips.

Don’t apply much pressure at all or you’ll ruin your soap’s shape. Just lightly run your fingertip over any imperfections.

What Size Should I Cut My Soap?

Most soaps are cut between ¾ and 1 ¼ inches thick. Really, it’s a matter of personal preference.

The nice thing about homemade soap is that you can customize things like size for your family’s needs.

Men often find a thicker bar is easier to hold onto in the shower while many women prefer a slightly thinner bar that fits comfortably in their hand.

Little children may have an easier time with small bars, so you may find yourself cutting several different sizes from each batch you create, and there’s certainly nothing wrong with that.

The decision is completely up to you.

You should know that the thicker the soap bars are, the longer it will take for the water to completely evaporate, and cure time will be greater.

Not a big deal; just give those chunky bars some extra cure time before using.

What Is the Best Soap Cutting Method?

If you were to ask 10 different soap makers what their preferred cutting method is, you would likely get 10 unique answers.

There are thousands of recipes for making soap and tons of different molding options. When you add personal preference to the mix, well, let’s just say that there really is no one right way to cut soap.

All the various tools and methods do have basically the same result – you wind up with multiple bars that are convenient to hold in your hand.

Let’s look at some of the most popular soap cutting techniques.

You may find one that you like right away, or you may be motivated to make your own. Either way, you’ll get that big loaf of soap sliced into usable bars in no time.

Knife

Those with a steady hand may want to simply use a knife to cut their loaves into bars.

To make nice, clean cuts, you’ll want a sharp, smooth (not serrated), thin-bladed knife – the less tapering on the blade, the better.

Freehand cutting may not produce identical, symmetrical bars, but that really doesn’t matter if you’re only making soap for personal use.

One tip is to make tick marks on a piece of cardboard in 1 inch increments. Line up your soap directly in front of the tick marks, and use them as a guide when cutting.

Soap Cutting Box

Believe it or not, you can purchase a device designed specifically for cutting soaps.

A wooden soap cutting tool is a box with precut grooves to guide your knife or cutter straight down through the soap.

This eliminates the chance of cutting slanted or crooked bars, occurrences that happen often when freehand cutting.

You’ll soon discover that many knives are too thick to fit in the grooves. To get around this problem, most soapers use a dough scraper.

I’ve found they do a fantastic job as they’re thin enough to fit, yet sturdy enough to resist bending.

They leave behind a nice, clean-cut with no drag marks that you might see with other knives.

If I could go back in time, I’d purchase a cutting set that comes with a mold, liner, cutting box, dough scraper and crinkle cutter.

Alternatives

A plastic miter box works nearly as well as a soap cutting box.

I used one of these for years and never had any issues. As with the cutting box, you’ll want to use a dough scraper.

I’d also recommend cutting a piece of cardboard to fit the bottom to help you glide your soap smoothly toward the knife and avoid damaging the bottom of your loaf.

If you enjoy DIY projects, you could easily recreate a soap cutting box in about an hour or two.

Soap Deli News has an easy-to-follow tutorial if you need some guidance or exact measurements.

Wire Cutters

There are fancy multi-wire soap cutters available on sites like Etsy, or you can use a multi-purpose wire cutter designed for slicing cheese, bread, and other fairly soft objects.

Note that this method will work best on soap that is still relatively soft, and harder soaps may cause the wire to break.

Cookie Cutters

If you have a large, thin block of soap, standard cookie cutters could be used to make a wide variety of shaped soaps.

Any leftover soap could be rebatched using the hot process method or cut into small pieces for use as embeds in future soaping projects.

What About Large Slabs of Soap?

Larger slabs of soap are a bit trickier to cut accurately, but it can be done.

Your best bet will be to use a tape measure or yardstick to measure evenly spaced intervals on opposite sides of your slab.

Either cut a small nick to mark the spots or place the soap on cardboard before beginning and mark the spots on the cardboard.

Working on one interval at a time, line up a yardstick on top of the slab to connect two opposite marks and lightly run your knife alongside.

This line will be where you will cut. With your dough scraper, cut through that line all the way down the length of your slab.

Repeat this process for all remaining guide marks until you are left with identical loaves of soap.

You may then proceed to cut the loaves as you normally would.