Inventory Accuracy Formula, by Item and by Value

Inventory accuracy measures how closely your records match what's actually on the shelf. There are two useful formulas. By item: the number of items whose count matched the record (within a tolerance you set) divided by the items counted. By value: one minus the total of the differences, ignoring whether they're up or down, divided by the recorded value. In the week worked through below, 17 of 20 items matched, 85% item accuracy, while the differences came to about $130 on $4,200 of recorded stock, about 97% value accuracy. Both matter: item accuracy shows how often the records are wrong, value accuracy how much it costs. Below are both worked through, a sensible target, the usual causes, and how to raise it.

The short version

• Item accuracy = items within tolerance ÷ items counted.
• Value accuracy = 1 − (sum of absolute differences at cost ÷ recorded value).
• Set a tolerance per item: exact for jars, a small percentage for flour.
• Use absolute differences: a shortage and a surplus don't cancel.
• Many businesses aim for 95% or better by item; start by measuring.
• Errors usually come from movements nobody recorded.
• TaroStack shows each difference's value before you post a count. More below.

The formulas

Item accuracy   = items counted within tolerance ÷ items counted
Value accuracy  = 1 − (Σ |counted − recorded| × unit cost) ÷ Σ recorded value

The bars around the difference mean "ignore the sign". If you added the differences as they are, 7 lb of flour short and 300 pouches over would partly cancel, and the records would look better than they are.

A week's count, worked through

Windward Roots, the made-up taro business I use in these examples, counts 20 items every week. Seventeen matched within tolerance. The three that didn't:

Item accuracy    17 ÷ 20 = 85%
Value accuracy   1 − ($129.64 ÷ $4,200 recorded) = 96.9%
Net difference   −$7.84 − $28.80 + $93.00 = +$56.36

The net says the stock is $56 better than the records; the absolute total says $130 of the records were wrong. The pouch surplus is probably a receiving or count mistake (300 pouches is a carton and a bit); the cream is probably waste nobody recorded. Each points to a different fix. How to work out a single item's variance, and its cause, is in inventory variance formula.

Tolerances

What a good number is

Many businesses aim for 95% or better by item, and higher by value, but the first job is to measure where you are and watch the trend. An 85% that rises to 92% in two months is doing better than a 95% nobody checks. Count the expensive and fast-moving items most often: they move the value figure and they're where mistakes cost most. A form for weekly counts is in cycle count form.

Where the differences come from

The full list of reasons records drift is in why inventory does not match.

Where this stops working

Measuring accuracy by hand means comparing a count sheet with a spreadsheet line by line, pricing each difference, and remembering to use absolute values. Most weeks nobody does it, so the count gets typed in over the records and the accuracy, and the cause, disappear with the old numbers.

How TaroStack does it

TaroStack makes every count a measurement of accuracy, not only a correction.

Each difference has a value before you post. Counts run on a phone, even in the walk-in with no signal, by shelf, with scanning if you like. Before the count is posted, TaroStack shows each difference and what it's worth at cost, so the $93 of pouches and the $28.80 of cream are on screen while you can still recount them.

It suggests what to count. TaroStack suggests what to count first: what it would cost to be wrong, times how much has happened since anyone looked. So the weekly 20 are the 20 that matter, which is how value accuracy rises fastest.

And the causes get fixed. Every adjustment carries its reason (expired, spoiled, damaged, sample, found, correction), so waste is recorded as waste instead of turning up as a count difference, and the losses report shows each reason's cost. Receiving against the order catches the extra carton at the door, units convert so a case isn't counted as an each, and stock can't go below zero by mistake.

Counts, adjustments with reasons, receiving and the losses report are on every plan, from $49 a month. The first 30 days are free, with no credit card. If you'd like a hand setting up, ask, and we'll do it with you.

Questions people also ask

How do you calculate inventory accuracy?

By item: items whose count matched the record within tolerance, divided by items counted. By value: one minus the sum of absolute differences at cost, divided by the recorded value. In the example, 85% by item and 96.9% by value.

What is a good inventory accuracy percentage?

Many businesses aim for 95% or better by item and higher by value. Measure where you are first, then work on the trend, counting expensive and fast-moving items most often.

Why use absolute values for inventory accuracy?

So shortages and surpluses don't cancel out. A $93 surplus and a $37 shortage net to +$56, but $130 of the records were wrong.

How can I improve inventory accuracy?

Record waste, batches and receipts as they happen, check deliveries at the door, set one counting unit per item, count by shelf, and count the items that matter most more often.