How to weigh liquor inventory in your bar or restaurant.
Weigh your liquor, wine, and draft beer for better inventory management.John Baker Bar Cop inventory expert extraordinaire
There comes a time in every man or woman's life, when you have to choose to weigh or not to weigh your bar inventory.
Ok, not everyone... but if you're a bar owner or manager, then it's a choice you will likely ponder one day.
And since you're here reading this now, today must be that day.
I'm not going to try and hard sell you on weighing your liquor bottles and kegs... I will just say that it's really important to weigh your products if you want an accurate inventory.
I am going to cover some common misconceptions on how to weigh your liquor inventory, why those ways are wrong, and how to weigh your liquor, wine, and draft beer the right way.
Oh and I'll also point you in the right direction on selecting the right kind of scale to use if you do decide to weigh your inventory.
Ok, ready? Great, let's get started...
There are few things that you absolutely need to weigh your liquor and draft beer:
1) A digital scale that weighs in ounces for liquor and wine bottles. And/or a scale large enough for kegs which will typically weigh in pounds/ounces.
2) A calculator, pen, and paper.
3) The density (specific gravity) for each product that you will be weighing.
I need the density for each product you say? Yes, yes you do. This is the part where most mistakes are made when weighing inventory.
The usual thought process is - I'll get a scale and weigh each product before a shift and then weigh it after.
If a bottle weighs 41.7 ounces in the beginning and 29.8 ounces at the end, then 11.9 ounces of product must have been used.
Another thought is to weigh a bottle and then subtract the bottle's tare weight (empty weight) to show how much liquor is left in the bottle.
Both ways seem logical, right?
They do, however both ways are wrong.
Here's the issue... fluid ounces and weight ounces are not the same thing.
Take Kahlua as an example: a 750 ML bottle of Kahlua holds 25.4 fluid ounces, however if you weighed just liquid.. . would it weigh 25.4 ounces?
No, the 25.4 fluid ounces of Kahlua would actually weigh substantially more than 25.4 ounces.
Why? Because of the density. Think of density as how thin/light or thick/heavy a product is.
As a starting point water has a density if 1. Liquor that is 80 proof is thinner or lighter than water, so it has a smaller density - in the .9 range.
Liqueurs and cordials are going to be thicker or heavier than water, so their densities will be larger than 1.
A product's density is how bartenders are able to layer shots. Lighter liquors will float on top of heavier ones.
Ok, so what does all this density stuff mean?
When you weigh liquor, wine, draft beer, or anything that has a density higher or lower than 1, you have to adjust for the density of the product for an accurate inventory.
One last point about densities - a density is a dynamically changing number.
That means a product's density will fluctuate based on temperature. If you weigh a product in the morning and then again at night in a room where the ambient temperature has changed, that can raise or lower the density slightly.
When weighing inventory, there will always be a margin of error. Typically that margin of error (which takes density changes into account) is 2% and under.
This is why weighing your bar's inventory is by far has the highest accuracy of any inventory method.
In comparison, eye-balling (now being called weightless inventory by some of the eye-balling inventory apps) has an average margin of error of about 15%.
The difference in accuracy is huge!
Ok, that was density information overload. Let's get back to learning how to weigh your inventory.
At this point you should have everything you need: a scale, calculator, pen, paper, and product densities.
The first thing you need to do are some important calculations for each product so when you weigh, you're converting weight ounces back to fluid ounces correctly.
1) Use your scale and weigh a full bottle of each product. You will need each product's full bottle weight (and full keg weights if you are weighing kegs) to find out the product usage.
2) Next you need to calculate each product's adjusted fluid ounce size based on the density. Bottle size (fluid ounces) x density = adjusted bottle size.
3) Then calculate the bottle tare weight based on that adjusted bottle size. Full bottle weight - adjusted bottle size = bottle tare.
You're now all set to start weighing.
Place a bottle on the scale and record the weight. Bottle weight - tare weight = fluid ounces in bottle.
To calculate your usage for each bottle, subtract the ending weight data from the starting weight data.
It's important to remember to keep track of new bottles that are added between the start and end.
If you weigh your bottles at the beginning of the day and your bartender goes through 2 bottles and ends with a different open bottle at the end of the day, you will have to factor in the added bottles to get the actual usage.
This is a good starting point when you want to weigh your liquor inventory and there are a lot more calculations you can do to learn things like how many shots were poured, your variance due to theft, etc.
All scales are not created equal.
Now that you know what you need and how to weigh your liquor, wine, and draft beer inventory, let's talk about scales for a minute.
If you decide to weigh, invest in a good quality scale. There are a lot of digital scale options on the market and when it comes to scales you really do get what you pay for.
The cheaper the scale, the easier the internal part will break when you repeatedly put bottles or kegs onto it. A cheap scale may last a few months - where high quality weigh scales should last years.
You might save a few bucks in the beginning, but over time replacing those cheap scales will add up and end up costing you more.
More importantly is getting a scale that will maintain it's accuracy.
All scales need to be calibrated at some point, but cheap scales can fall out of calibration by simply moving it. Good scales will hold their calibration when using it in harsh bar and restaurant environments.
If you are using a cheap scale that can fall out of calibration during the weighing process, you'll never know if the weights you're getting are accurate or not.
So again, if you are going to use a scale to weigh your bar's inventory - invest in a good quality one.
One last point on scales - make sure that the scale you use has a weight capacity that is at least 2 times greater than the heaviest product you will be weighing.
For bottles, this would be a minimum weight capacity of around 10 pounds and for kegs a minimum weight capacity of 320 pounds. When it comes to keg scales, the higher the weight capacity the better.
Why is weight capacity so important?
When you are weighing liquor bottles and kegs, you are always placing the bottle or keg on the scale with a greater force than the actual product weight.
If you have a scale with a weight capacity of 5 pounds, and you are weighing bottles in the 4-5 pound range... the force placed on the scale may exceed the scale's weighing capacity, damaging it prematurely.
I hope I've given you a good starting point on weighing your inventory and if you have any questions about the process, ask away in the comments section below.