MRP for small business: what it is, when a spreadsheet still wins

Material requirements planning (MRP) is software that works backward from what you plan to sell to what you need to buy and build: it takes a forecast or order book, explodes it through your product recipes into component demand, nets off what you already hold, and tells you what to order and when. If you resell finished goods, you don't need it — Shopify plus a buying list covers you. If you make or assemble things — embroidery kits, kitchen knife sets, bath bombs — MRP logic is the correct way to think about purchasing, and the question is whether you need software to run it. This article explains the mechanics with a worked mini-run, then gives the honest decision for a business at your size.

The three inputs MRP runs on

Every MRP system, from a $50k tier to a spreadsheet, needs the same three things:

1. What you plan to sell or build. A forecast, a schedule of production runs, or actual open orders. This is the master schedule — MRP never invents it; you feed it.
2. What each product is made of. The recipe: for each finished good, the components and quantities per unit, plus how long assembly takes. This is the bill of materials, and it's where most small-business MRP projects die — not because the software is bad, but because no one has written down the recipes.
3. What you already have and what's coming. Current component stock, on-order quantities, and supplier lead times per component.

The output is component-level order timing: "buy 400 zipper pulls by the 12th, cut 60 sheets of waxed canvas next week." The deep mechanics of the component side — how to count and value raw materials you hold — live in our raw materials inventory article, and the goods stuck between parts and finished product are WIP inventory; this article stays on the planning layer.

A mini-run, dissected as a post-mortem (small enough to do in a spreadsheet)

The worked numbers below are real enough to verify, and they're framed as a post-mortem: a knife-roll launch that slipped, taken apart to see how the planning failure happened. You make embroidery kits that sell on Shopify, plus assembled knife-roll bundles. Two products, four components. Builds start the first week of November; your numbers at the end of October:

• Kit A: 1 canvas panel, 6 floss skeins, 1 needle pack, 1 instruction card. Planned build: 120 kits over the next 4 weeks (30/week).
• Knife roll: 1 waxed canvas sheet, 8 zipper pulls, 2 leather straps. Planned build: 40 rolls this month.

Current stock and open orders:

Run the explosion:

• Kit A needs: 120 panels, 720 skeins, 120 needle packs, 120 cards. Net of stock: panels 120 − 90 = 30 short, and the 100 arriving Nov 10 covers it (check timing: builds run 30/week, so the 90 on hand covers weeks 1–3; the week-4 build of 30 is what the Nov 10 arrival has to cover — and it does, with a few days to spare). Skeins: 720 − 400 = 320 to order now (14-day lead lands in time). Needles: 120 − 200 = covered. Cards: covered.
• Knife rolls need: 40 sheets, 320 pulls, 80 straps. Sheets: 40 − 25 = 15 to order now — lead time is 21 days and builds start Nov 2, so the order had to go out by ~Oct 12. That's the post-mortem's whole point: this is the PO that didn't get sent, and "we have 25, feels like plenty" is exactly how a 21-day component quietly delays everything. Pulls: covered. Straps: 80 − 30 = 50 needed; 60 arrive Nov 24 — covered only if the Nov 24 arrival holds, so flag it.

Total output: two purchase orders (320 skeins, 15 sheets) and one watch-item. That's the entire core of MRP: explode, net, time. Systems add capacity limits, lot sizes, scrap factors, and rescheduling logic — valuable at scale, but the explosion-net-time loop is the substance.

When a spreadsheet beats MRP software

Be honest about scale. If your business looks like this, a spreadsheet you rebuild monthly does the same job as an MRP tier:

• Under ~20 recipes, few components each, most shared between products.
• Builds on a weekly rhythm you control, rather than a chaotic order-driven schedule.
• One person owns purchasing and knows the suppliers by name.
• Component SKUs under ~150 total — countable in an afternoon.

Your spreadsheet version is literally the table above: recipes × planned builds − stock + on-order, refreshed when plans change. The spreadsheet approach to Shopify inventory extends naturally to a components tab. The advantages are real: nothing to implement, every number inspectable, and no subscription fighting your carrying cost.

The spreadsheet breaks when any of these turn true:

• Recipes multiply or churn — 50+ bills of materials, frequent reformulations, and version confusion ("which recipe was the Q3 kit?").
• Components are shared across many products — allocation conflicts (this sheet of canvas goes to the kit or the roll, not both) become daily arithmetic.
• Capacity and scheduling matter — when workstation time or batch sizes constrain what you can build, plain explosion isn't enough.
• More than one person needs to run or audit the numbers.

At that point the software question isn't "should I buy MRP" but "which recipes and components do I need to clean up first" — because the software will faithfully explode garbage recipes into garbage orders.

The honest ERP framing for your size

Two scope notes stated plainly:

• Shopify alone is not an MRP. As of October 2026, native Shopify handles finished-goods stock, POs, transfers, and counts; it has no bill-of-materials engine, so it can't convert "sell 120 kits" into "buy 320 skeins." Bundle-style inventory on Shopify tracks component availability without doing component purchasing for you — the kitting mechanics are their own topic.
• InventoryX doesn't do MRP, and won't pretend to. We're a read-only planning layer for resold finished goods: per-SKU days-of-cover, a weekly buying list, draft POs. BOMs, raw materials, and work orders are ERP territory and out of our V1 scope — if you build things, run your component math in a spreadsheet or a dedicated MRP tool, and let Shopify track the finished goods you produce.

The cheapest honest test of whether you need MRP software: run the explosion above by hand for your two best-selling builds. If it takes under an hour and you trust the result, you've just built this month's MRP for free. If it takes a day, breaks on shared components, or you can't state the recipes confidently — that's the software trigger, and also the signal that the recipes need writing down regardless of tooling.

Common questions

What is MRP in simple terms? Material requirements planning: software that converts your sales or production plan into component-level purchase timing. It explodes each planned product through its recipe (bill of materials), subtracts what you already hold and what's on order, and schedules the buys against supplier lead times — so the parts arrive before the build, not after.

Does a small business need MRP software? Not below roughly 20 stable recipes and a couple hundred component SKUs run by one person — a spreadsheet running the explode-net-time loop monthly does the same job with zero implementation cost. The triggers for real MRP are recipe churn, heavy component sharing across products, capacity scheduling, and multiple people needing the same numbers.

What's the difference between MRP and inventory management? Inventory management tracks and reorders what you sell; MRP plans what you need to make it. If you resell finished goods, inventory management plus reorder points covers you. If you manufacture or assemble, you need MRP logic on the component side on top of finished-goods tracking — they answer different questions about different stock.

What is a bill of materials and why does it matter? The recipe for one unit of a product: components, quantities, and assembly steps. It's the input that makes MRP possible — the software can't plan what you haven't written down. In practice, most failed small-business MRP implementations failed here: the tool exploded inaccurate or outdated recipes into confident, wrong purchase orders.

Can Shopify do MRP? No, as of October 2026. Shopify natively tracks finished-goods inventory, purchase orders, and counts, but has no bill-of-materials or work-order engine, so it can't translate a production plan into component purchasing. Makers either run the explosion in a spreadsheet or use a dedicated MRP tool alongside Shopify, which continues to track the sellable goods.

Next step

Write down the recipe for your single best-selling product — every component, quantity, and each supplier's real lead time from your last PO (quotes lie; arrivals don't). Then run one month's explosion by hand, exactly like the worked example above. That hour tells you which side of the spreadsheet-or-software line you're on, and the recipes you write down are the asset either path needs next.