Setting Your Par Level: 7 Numbers Behind Never Running Out

Every kitchen knows this moment: by quarter to nine the fish of the day is gone, or on Sunday night three portions of game end up in the bin. Two completely different evenings — and yet it's the same mistake: nobody put a number against the guess.

How much do you prep of a dish? Most kitchens answer with a feeling: “we always make a bit extra”, or “we count the bookings and guess the rest.” That feeling isn't stupid — it's years of experience — but it only answers half the question. Prepping too little costs you a sale you'll never get back. Prepping too much costs you an ingredient you've already paid for. They're two opposite mistakes, and the right amount sits precisely between them.

That tipping point isn't a feeling, it's a sum — and it's the same sum a newspaper vendor has used for a hundred years to decide how many papers to order, and a clothing shop uses to decide how many winter coats to buy in. It's known as the classic inventory problem: what does a missed sale cost, what does a leftover cost, and how do the two weigh against each other.

This guide walks through the seven numbers one by one: what a missed sale actually costs you, what a wasted portion actually costs you, the ratio between the two, your average night, how much that night swings, your recommended stock level, and what a wrong guess costs you per year. At the bottom, you plug in your own dish.

Everything runs in your own browser: nothing is sent anywhere and nothing is stored. The calculator gives you a guideline number, not a prescription — your supplier, your kitchen and your guests know the dish better than any formula does.

Why running out and throwing out are the same mistake

The two problems don't feel the same. Running out is visible and uncomfortable: a guest hears “no”, the room sees it, and someone has to explain it. Throwing food out is quiet — it happens after closing, alone, in a bin nobody checks. That's why one mistake feels far worse than the other, and that feeling pushes most kitchens toward always prep enough. Which is exactly where it goes wrong: this isn't a moral question, it's a sum — and the sum doesn't always give the same answer.

Both mistakes cost money, just not the same amount. A missed sale costs you the profit you would have made on that plate — the whole margin, gone. A wasted portion only costs you what the ingredient cost you — the rest of that margin you never spent in the first place. For most dishes, the first cost is bigger than the second, which is why “better a bit too much” is usually the right instinct. But not always: with an expensive, fast-perishing ingredient, the ratio can flip — and then that same instinct becomes your most expensive habit.

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The 7 numbers, and what each one tells you

They build on each other. The first two are five minutes of arithmetic. The last two are where the real money is.

1. What one missed sale actually costs you

A guest wants the salmon, you're out of salmon. Some order something else instead — usually something cheaper — and some say thanks and move on to the next dish on the menu, or the next restaurant. What you lose isn't the revenue on that plate, it's the margin on it: the menu price excluding VAT, minus what the ingredient cost you.

A dish priced at €27, ingredient cost €11: once VAT is stripped out, that missed sale costs you €13.55 in lost margin. That's what every missed portion actually costs you — not the €27 on the menu, which is the overestimate almost everyone makes, and not nothing either, which is the underestimate.

Call this number your underage cost: what disappears every time you're one portion short. The higher this number, the more a missed sale hurts — and the more it pays to keep a little extra ready.

2. What one wasted portion actually costs you

On the other side sits the portion nobody orders. That doesn't cost you the margin — you never earned that margin — it only costs you what you already paid for it: the ingredient cost, and nothing more.

This is a classic mistake worth naming on its own: some owners price the loss at the menu price, and end up overestimating what waste costs by two or three times. A wasted portion that cost €11 to buy in feels, to the chef, like “€27 in the bin” — and that feeling pushes tomorrow's prep even more cautious, which is exactly the wrong direction.

Call this number your overage cost — in this example, €10.50. For most dishes it's smaller than the underage cost from step 1, and that difference is exactly why “better a bit too much” is usually the right call. With an expensive, fast-perishing ingredient — lobster, a pricey fish, game — that isn't always true, and you only see it once you set the two side by side.

3. The ratio between the two — your target percentage

Put the two numbers side by side and you get one percentage that sums everything up: underage cost divided by the sum of underage cost and overage cost. That percentage tells you what share of nights you want to have enough on hand — your target ratio.

For the dish above: €13.55 divided by (€13.55 + €10.50) is 56%. For a side like fries — cheap, durable, high margin — that number often runs above 80%: almost never running out is the right call, because one portion too many costs almost nothing. For lobster — expensive to buy, thin margin relative to that cost — the number can drop below 40%: occasionally saying “no” is cheaper than structural leftovers.

This is the number the whole guide turns on, and it's never the same for two dishes on your menu. The calculator further down works it out automatically once you enter your price and your cost; the graphic below shows how three very different dishes land on three very different ratios.

Same sum, three totally different outcomes — set by how much a missed sale weighs against how much a wasted portion weighs.

83% Cheap and durable. Almost never running out is the right call here.

56% Average margin, spoils fast. A healthy balance between the two.

36% Expensive to buy, thin margin. Occasionally selling out is cheaper here.

The further the balance tips left, the higher the target ratio — and the more generously you can afford to prep. The further right, the more careful you should be. No two dishes on your menu should get the same rule of thumb.

4. Your average night

The target ratio tells you how often you want to have enough. To know how much that actually is, start with the simplest of the seven numbers: how much you sell on average, on a night the dish is on the menu.

Add up the last two to three weeks — not one night, because one night is an outlier, not an average — and divide by how many times it was offered. Twenty portions a night is a solid starting point for an evening dish that's on the menu every day; a weekend special usually runs on a smaller number, over fewer nights.

This number alone isn't enough to plan on — two dishes with the same average of twenty portions can behave completely differently, which brings you to the next number.

5. How much that night swings

A dish that sells between eighteen and twenty-two portions every night is easy to plan for: prepping twenty covers you almost every time. A dish that does eight portions one night and forty the next isn't — the same average of twenty is hiding a completely different risk.

You don't need to measure this precisely to act on it. Look at your own numbers from the last few weeks and sort the dish into one of three groups: predictable (the nights sit close together — a regular evening dish, a side), normal (the usual swing of a main course that depends on who's in that night), or wild (a weekend special, something weather-dependent, something tied to one event or party).

The wilder the dish, the bigger the buffer you need above your average to hit the same target ratio — and that's exactly what the next number works out for you.

6. Your recommended stock level

This is where the previous four numbers come together: your average night, plus a buffer that grows as the dish gets wilder and your target ratio climbs. That recommended amount — your stock level, or in trade terms, your par level — is the number that belongs on your prep sheet, not the average from step 4 and not a fixed margin “to be safe.”

Take the dish from before: an average of twenty portions a night, normal swing, a 56% target ratio. The sum works out to a recommended stock of twenty-one portions — a buffer of one, not the five or six that “to be safe” usually produces. For a wilder dish with a higher target ratio, that buffer grows; for a predictable dish with a lower target ratio, it shrinks close to zero.

That's exactly the mistake this number fixes: most kitchens use the same rule of thumb — “plus twenty percent” — for every dish on the menu, whether it's fries or lobster. The number above is different for every dish, and that's the whole point.

Catch of the day, twenty portions average a night, normal swing. The dark zone is your buffer — just enough to have enough on 56% of nights, not a portion more.

average night: 20 recommended stock: 21

your buffer: A wilder dish stretches the curve wider — the same buffer then covers fewer nights, so the recommended level rises to hit the same target ratio. A predictable dish does the opposite: the curve narrows and the average is almost enough on its own.

7. What a wrong guess costs you per year

The last number is the one that changes the conversation: what does it cost to stick with your current guess instead of switching to the recommended stock level? You work that out by comparing the expected cost of missed sales and wasted portions at both levels, across a full year.

For the dish above — a kitchen that's been prepping twenty-five out of caution for years, instead of the recommended twenty-one — that difference comes to roughly €3,746 a year, for one dish, six nights a week. That's not a rounding error: it's four portions too many, night after night, that nobody ever ordered. Spread across a menu of ten dishes each running a little too generous or a little too tight, that's quickly enough to cover an extra staff member for a month.

This is also the number that settles the argument in the kitchen. “We'd rather make a bit extra” is an opinion; “that costs us roughly €3,746 a year in salmon nobody buys” is a fact everyone can agree on — or not, in which case you adjust the assumption until it does hold up.

Calculate it for your own dish

Fill in the five numbers for a dish on your own menu. The fields start out filled in with the catch-of-the-day example from this guide, so you can see straight away how it reads — overwrite them with your own.

You'll get your underage cost, your overage cost, your target ratio, your recommended stock level, and — if you fill in what you currently prep — what that guess costs you per year against the recommended level.

Two things to keep in mind when reading your result. The recommended level is never a fixed percentage above your average — it differs per dish, because the target ratio differs per dish. And the guideline number gets more reliable the more nights your average is built on: two weeks is a starting point, six weeks is a number you can plan around.

What to do with this this week, this month and this quarter

Reviewing your whole menu at once isn't realistic for anyone. This order works, because each step makes the next dishes faster.

This week — work through your two wildest dishes

• Pick the dish that runs out most often, and the dish that's leftover most often. Those are your two biggest opportunities.
• Put the underage cost and the overage cost side by side for both, and work out the target ratio.
• Compare the recommended stock level with what actually gets prepped right now.
• Adjust only these two dishes for now — not the rest of the menu.

This month — measure instead of guess

• Log how much sells of your five key dishes for two to three weeks, on every night they're on the menu.
• Look not just at the average but at the spread: which dishes swing wildly, which stay stable.
• Recalculate the recommended level for those five dishes using your real numbers instead of an estimate.
• Link this to your stock management, so the recommended level immediately becomes your reorder threshold.

This quarter — build it into your routine

• Bake the sum into your mise en place list, so every new dish on the menu gets a stock level from day one instead of a guess.
• Recalculate every quarter — a dish that was “wild” for a season can turn “normal” the next.
• Set your covers forecast alongside it: a busy weekend lifts your average for those nights only, not the whole week.
• Revisit your menu engineering: a dish that structurally runs into leftovers is sometimes simply a dish that can come off the menu.

The right amount is never a fixed percentage

Almost every kitchen that runs these numbers discovers the same thing: the rule of thumb they applied to every dish was right for maybe half the menu. For the other half, it was either too cautious — margin thrown away — or not cautious enough — missed sales nobody ever counted.

That's good news, because fixing it costs no extra staff and no new equipment. It costs two numbers per dish: what a missed sale costs, and what a wasted portion costs. Everything else — the target ratio, the buffer, the recommended level — follows automatically from those.

Start with the dish that bothers you most: the one that runs out too often, or the one that's leftover too often. Run the numbers once, and the next nineteen dishes on your menu go faster. For the bigger picture, your food cost control and your prime cost show you what all of this adds up to across the whole menu.