Tape a sheet of wet-or-dry sandpaper to a flat counter or a hardcover book, start at 400 grit and finish at 1000, and stroke the knife edge-first at about 15 to 20 degrees until you feel a small burr along the far side. Then flip and repeat, and finish with a few edge-trailing strokes on a belt or the back of a notepad. No sandpaper in the house? Turn a coffee mug upside down and use the rough unglazed ring on its bottom. Both work. The rest of the household tricks range from "fine for a touch-up" to "don't bother."
First: is it dull, or just bent?
A knife that cut tomatoes fine last week usually isn't worn out; its edge is bent over in places. That needs straightening, not grinding, and anything hard and smooth will do it. Run a quick check:
- Hold a sheet of printer paper by one corner and slice down it from heel to tip. Catches in a few spots mean a rolled edge. Won't bite anywhere means dull.
- Tilt the knife under a bright light with the edge facing you. A sharp edge is invisible. Bright glints along it are flat, worn spots, which Red Label Abrasives also uses as its light-reflection test.
If it's only rolled, five light strokes per side on the mug ring or along the spine of another knife (see below) will bring it back. If it's dull, you need to remove steel, so read on.
Every household method, ranked
| Method | What it is | What it can fix | Our verdict |
|---|---|---|---|
| Wet-or-dry sandpaper on a flat surface | Silicon carbide paper with real grit numbers | Very dull edges, even small chips at 220–400 | Best by far |
| Unglazed mug or plate ring | Fine fired ceramic | Moderately dull edges, burrs | Good, slow on very dull knives |
| Fine flat river stone or slate, wet | Natural stone, grit unknown | Dull edges if the stone is fine and flat | Good in camp, hit or miss |
| Spine of another knife | Hardened steel, smooth | Rolled edges only | Works like a honing rod |
| Leather belt, cardboard, jeans | Strop material | Burr removal and polish only | Great finishing step |
| Car window top edge | Unpolished glass | Light dullness | Works, awkward, risks the window |
| Brick or concrete | Coarse, uneven | Chips | Last resort, then finish finer |
| Aluminum foil | Soft metal | Nothing | Myth |
| Glass bottle rim | Glass, often chipped | Little | Skip it: glass splinters |
Holding the angle with no guide
Most kitchen knives want 15 to 20 degrees per side. Start with the blade straight up from the surface (90 degrees), tilt it halfway (45), then halfway again (about 22). Drop a touch lower and you're there.
A more exact check is the height of the spine. For a typical chef's knife about 50 mm (2 inches) tall at the heel, 15 degrees puts the spine about 13 mm off the surface and 20 degrees about 17 mm. That's why the popular "stack two coins under the spine" tip doesn't hold up on a kitchen knife: two US quarters are only 3.5 mm thick (the US Mint lists a quarter at 1.75 mm), which is closer to 4 degrees on that blade. You'd need a stack of about seven quarters for 15 degrees. The angle calculator works it out for any blade width.
Whatever angle you pick, color the edge with a marker before you start. After a few strokes, the ink shows exactly where you're grinding. The sharpie trick guide shows how to read it.
Method 1: sandpaper (the best)
- Lay the sandpaper on something flat and hard: a countertop, a pane of glass, a tile or a hardcover book. Tape the corners down. A soft surface lets the paper wrap the edge and round it.
- Wet the paper if it's wet-or-dry paper. 3M's listing says to use it with water to reduce clogging.
- Start at 400 grit for a dull knife, or 220 if it's chipped. Red Label Abrasives uses 220 or 400 to start and 1000 or 2000 to refine.
- Hold the knife at your angle, edge first, and push it across the paper from heel to tip in one sweep. Edge-first strokes are fine on sandpaper as long as the pressure is light; if the paper tears, switch to pulling the knife spine-first instead.
- Keep going on one side until you can feel a slight burr along the whole opposite side. Feel by sliding a fingertip off the edge from the spine side, never along it.
- Flip and do the other side until the burr moves back.
- Move to 1000 grit and repeat with lighter strokes, alternating sides every few passes.
- Finish with ten edge-trailing strokes per side on cardboard, the back of a notepad or a leather belt.
A 400 to 3000 grit wet-or-dry assortment covers everything from a dull edge to a polish, and single packs like 3M 400 grit are in most hardware stores. The same sandpaper-on-glass setup works for X-Acto and hobby blades.
Method 2: the bottom of a mug
Turn a ceramic mug or plate upside down on a towel. Look for the ring on the bottom that isn't glazed; it's rough to the touch. That ring is your stone.
- Hold the knife at 15 to 20 degrees with the edge against the ring. America's Test Kitchen uses 15 degrees.
- Draw the blade across the ring, heel to tip, in one smooth stroke. Five to ten strokes per side, alternating.
- You'll see gray metal streaks on the ceramic. That's steel coming off; wipe it away when you're done.
It's slow on a truly dull knife and the ring is short, so long knives take patience. For a midweek touch-up, it's genuinely good.
Method 3: a flat stone from outside
Look for a smooth, flat, fine-grained stone: slate, fine sandstone or a flat river stone. Avoid coarse granite and anything cracked or crumbly. Wet it, set it on the ground or a log so it can't move, and use the same strokes as sandpaper. Check your progress often; you don't know its grit, and a coarser stone than you expect will leave a rough edge. Finish on your belt.
Method 4: the spine of another knife
Hold one knife still with its edge pointing away from you, and draw the edge of the dull knife lightly along its spine at your angle, heel to tip, alternating sides. The hard, smooth spine acts like a steel honing rod: it straightens a rolled edge but removes almost no metal. Go slowly and keep your hands clear.
Method 5: belt, jeans or cardboard
These don't sharpen; they finish. After sandpaper, a mug or a stone, a few edge-trailing strokes on a tight leather belt, a pair of jeans laid flat, or the plain side of a cardboard box remove the burr, and that's often the difference between "sharpish" and properly sharp. Our how to strop a knife guide covers the stroke.
Car windows, concrete, foil and bottles
The top edge of a car window is unpolished glass and does abrade steel; Kent Rollins calls it his favorite trick. The strip is narrow, though, you're standing at an odd angle, and a slip scratches the glass or your hand. We'd use the mug first. Concrete steps and bricks are coarse and uneven: they'll take out a chip, then you need something finer. Aluminum foil is much softer than knife steel and can't remove metal, whatever the videos say; at best it bumps a rolled edge straight. And skip the glass bottle rim. Dalstrong's own guide warns about glass splinters on the blade, and a bottle rim is rarely smooth enough to do anything useful.
When it's worth buying a real sharpener
If you've done this twice, an inexpensive pull-through sharpener or a basic stone will save you time. The KitchenIQ Edge Grip is a carbide and ceramic pull-through for the kitchen drawer, the SHARPAL 101N is a pocket tool with carbide and ceramic slots plus a diamond rod, and the Sharp Pebble 1000/6000 is the beginner whetstone we see recommended most. Our picks for the best manual knife sharpener and the best knife sharpener for beginners go further, and once you have a stone, how to use a whetstone picks up where sandpaper leaves off.
Methods compared against America's Test Kitchen, Red Label Abrasives, Kent Rollins, Dalstrong and Perkin Knives, read October 13, 2026. Quarter thickness from the US Mint's coin specifications; spine heights calculated. Product details from Amazon listings checked the same day. How we research · Affiliate disclosure