Inventory calculators for Shopify brands
Free calculators for every key inventory metric — safety stock, reorder points, EOQ, days of inventory, and more. Each one includes the formula, worked examples, and Shopify-specific tips.
All calculators
Pick the metric you need to calculate. Each calculator includes the formula, variable definitions, step-by-step examples, and common pitfalls to avoid.
safety stock calculator
Safety Stock Calculator
Calculate your ideal safety stock level instantly. Use the free Synplex safety stock calculator to protect against stockouts, understand Z-values, and see worked examples for Shopify inventory planning.
Calculatereorder point calculator
Reorder Point Calculator
Calculate the exact reorder point for every SKU. Use the free Synplex reorder point calculator with worked examples, safety stock integration, and Shopify-specific tips.
CalculateEOQ calculator
EOQ Calculator (Economic Order Quantity)
Calculate the most cost-efficient order quantity for any SKU. Use the free Synplex EOQ calculator with worked examples, holding cost guidance, and Shopify tips.
Calculateinventory turnover calculator
Inventory Turnover Calculator
Calculate your inventory turnover rate and days of inventory (DSI). Use the free Synplex inventory turnover calculator with industry benchmarks and Shopify-specific guidance.
Calculatesell-through rate calculator
Sell-Through Rate Calculator
Calculate your sell-through rate by SKU or collection. Use the free Synplex sell-through rate calculator with industry benchmarks, worked examples, and Shopify tips.
Calculatedead stock calculator
Dead Stock Calculator
Identify dead stock and quantify how much cash is trapped in non-moving inventory. Use the free Synplex dead stock calculator with inventory aging logic and Shopify-specific guidance.
Calculatedays of supply calculator
Days of Supply Calculator
Calculate how many days your current inventory will last at your current sales velocity. Use the free Synplex Days of Supply calculator with worked examples and Shopify-specific guidance.
Calculateinventory carrying cost calculator
Inventory Carrying Cost Calculator
Calculate your inventory carrying cost percentage and see how much it costs to hold stock over time. Use the free Synplex inventory carrying cost calculator with worked examples and Shopify-specific guidance.
CalculateWhat every calculator includes
These aren't just formula pages. Each calculator is structured as a complete reference for Shopify merchants who want to understand the metric, not just copy a number.
Formula variants
Multiple versions of each formula for different data availability — basic, intermediate, and advanced — so you can use whichever fits your situation.
Variable definitions
Every symbol and input defined clearly with units and practical guidance on where to find the number in your Shopify data.
Step-by-step examples
Worked scenarios with realistic inputs and annotated calculation steps, so you can follow the logic and adapt it to your products.
Industry benchmarks
Reference ranges by category so you can tell whether your result is healthy, too lean, or overstocked relative to similar businesses.
Common mistakes
The most frequent errors merchants make when calculating each metric — and the fix for each one.
Shopify-specific tips
How to apply the formula given Shopify's data model, multi-location inventory, and the way Synplex surfaces each metric automatically.
Why accurate inventory calculations matter
The core problem: Every inventory decision — when to reorder, how much to order, how much safety stock to hold — flows from a small number of input metrics. Wrong inputs produce wrong decisions, which produce stockouts or dead stock.
Most Shopify merchants calculate these metrics in spreadsheets using rules of thumb. The formulas on these pages replace guesswork with a systematic approach. Once you understand the inputs and relationships, you can configure Synplex to track and act on them automatically — so you stop running the numbers manually every week.
Related resources