A petty knife and a paring knife are both the small knife next to the big one, and in English the two names are often used as if they meant the same thing. They overlap, but they are not the same knife. The clearest way to tell them apart that I found comes from a knife shop in Sakai, and it is not about the shape. It is about whether the knife is used on the cutting board or in your hand.
What a petty knife is in Japan
Petty comes from the French petit, small. In Japan it is one of the standard Western-style knives, along with the gyuto and the sujihiki, and Japanese shops treat it as the second knife a home kitchen should have.
Sakai Ichimonji Mitsuhide, a knife shop in Sakai, says on its Japanese page that petty knives are in most cases 125 to 150mm long. Its summary at the end of the page gives 120 to 150mm as the basic range.
A Western paring knife is shorter. The paring knives listed on Hocho-Knife, a Japanese knife retailer, are 76 to 100mm. The 90mm paring knives from Global and Masahiro are typical.
So the plain answer to the length question is that a petty knife is usually 120 to 150mm and a paring knife is usually under 100mm.
The question the shop asks first
Ichimonji does not tell you to choose by length. It tells you to think about how often you will use the knife on the cutting board, and how often you will hold the food in your hand and work without a board, peeling, or turning vegetables into neat shapes for French cooking. Then it gives the sizes that fit each case.
If your kitchen is small and the petty is going to be your all-purpose knife, the shop recommends 150mm. A short knife is easy to move around in a narrow space, and it says the 150mm petty is popular in homes as a replacement for a santoku.
If you are a cook who prepares large amounts of vegetables and peels more than you slice, it recommends 125mm, and says professional cooks often buy that size. The reasoning is that a professional already has a gyuto for most of the work on the board.
And if you will never use the knife on the cutting board at all, it suggests a 90mm petty, a peeling knife or a chateau knife, the small curved knife cooks use to turn vegetables.
That last case is what most English-speaking cooks mean by a paring knife: a short blade for work in the hand. A Japanese shop puts it at the short end of the petty range, and treats the longer petty as a knife for the board.
The name does not follow the length
On Hocho-Knife, the line between the two names is drawn by the maker, not by the size. Sakai Takayuki calls its 90mm Grand Chef a petty knife. Masahiro calls its 90mm MV-H a paring knife. Global calls its 90mm and 100mm GS knives paring knives. Sakai Takayuki itself uses both words: the same 45-layer mirrored Damascus series has a paring knife at 80mm and a petty knife at 135mm.
If you are comparing listings, read the blade length and ignore the word. A 90mm knife does the same job whichever name it carries.
Petty knife vs utility knife
On Hocho-Knife every petty knife is listed as Petty Knife, with Utility in brackets after it, from 90mm up to 180mm. The retailer treats the two names as one category, and I have not found a Japanese source that draws a line between them. If a listing says utility knife, check the length and the edge, and read it as a petty knife.
Steel: stainless is the safe default
The same shop has a separate page on choosing a petty knife, and its first piece of advice is about steel. If you have no strong preference, it says, stainless is the safe choice for a petty knife.
The reason is the food. A petty knife spends a lot of its time on lemons and other citrus, fruit and garnishes, which are acidic, and carbon steel rusts quickly on them. Rust care is needed with any carbon knife, but with a petty knife you would need more of it. The shop adds that stainless is usually harder to sharpen than carbon steel, but a short blade takes less work, so the downside is small.
I agree with this. If you already own a carbon gyuto and enjoy looking after it, a carbon petty is fine. If this is a second knife you want to pick up for a lemon without thinking, buy stainless. What patina and rust look like on a carbon knife is in patina or rust.
The petty is the cheapest way to own a hand-forged knife
One more point from the Ichimonji page that I had not seen in English. A hand-forged petty takes almost the same work in the forge as a gyuto made the same way. But in the Japanese knife trade, the price is set in proportion to the blade length, so the petty sells for comparatively little.
In other words, if you want a knife forged by hand in Sakai and do not want to pay gyuto prices, the petty is the shape to look at. I wrote about what hand forging changes, and what it does not, in hand-forged vs machine-made.
The same series in three lengths
To show what length costs on its own, I looked at one series made in all three sizes, the Sakai Takayuki Grand Chef, on Hocho-Knife on 1 October 2026. All three are double-edged, so they work in either hand, and all three use a high carbon stainless steel from Bohler-Uddeholm, listed at about HRC 61 to 62.
The 90mm weighs 60g and costs $88.99. The 120mm weighs 70g and costs $96.99. The 150mm weighs 80g and costs $102.99. All three were in stock.
From the shortest to the longest the difference is 14 dollars, so price should not decide the size. How you will use the knife should.
Which one to buy
If you already have a gyuto or a santoku and want a small knife for fruit, garnishes and small jobs on the board, buy a 150mm petty. It is the size Ichimonji recommends for a home, and it can stand in for the big knife on a busy day.
If you cook a lot of vegetables and want something more nimble, the 120mm is the professional choice the shop describes.
If you mostly peel apples in your hand, hull strawberries and never put the small knife on the board, buy a 90mm knife, and do not worry whether the listing calls it petty or paring.
If you do not have a main knife yet, start there. The sequence I would buy in is in how to choose a Japanese knife, and the choice between the main shapes is in gyuto vs santoku vs bunka.
The three knives
For most readers: the Sakai Takayuki Grand Chef petty 150mm at $102.99. Stainless, double-edged, 80g, in stock on 1 October 2026.
For cooks who prep a lot of vegetables: the Sakai Takayuki Grand Chef petty 120mm at $96.99. Same steel, in stock on the same date.
For work in the hand, the size most people call a paring knife: the Sakai Takayuki Grand Chef petty 90mm at $88.99. Also in stock on 1 October 2026.
Disclosure
I have four approved affiliate partnerships: two with knife retailers, Hocho-Knife and SharpEdge, and two with Japanese language-learning companies unrelated to knives. This page carries three tracked links, all to Hocho-Knife. At about 10 percent, that is roughly 9 to 10 dollars for each knife. The three differ by only 14 dollars, so the one I recommend to most readers is not the one that pays me most by any meaningful amount. My full affiliate disclosure is here.
Sources, checked on 1 October 2026: the Sakai Ichimonji Mitsuhide Japanese pages on the petty knife and on choosing a petty knife, and the Hocho-Knife product pages and listings for the Sakai Takayuki, Masahiro and Global knives above.