Setting min/max stock levels for lawn mower parts that actually hold up

Tuesday morning. Customer walks in with a Toro Timemaster that needs a drive belt. You know the part — you've installed thirty of them this year. You walk to the shelf. Empty. You call Stens. Two days out. You call Rotary. In stock. You pay expedited shipping. The customer now gets their mower Friday instead of Tuesday, and you ate $18 in shipping.

That happens because your lawn mower parts inventory was set up by guesswork, not by math. Good inventory is not about having everything — it's about having the right 200 parts at the right levels so you never have this conversation again.

Here's how to set min/max levels that actually hold up.

The basic formula, and why gut feel is wrong

The traditional formula every parts manager learns is:

• Min = (weekly usage) × (lead time in weeks) + safety stock
• Max = min + (reorder quantity)

The problem with gut feel is that shop owners underestimate the fast movers and overstock the slow movers. You remember the time a customer needed an obscure carb kit and you didn't have it — so you buy three of them. Meanwhile, the $4 blade bolt you sell ten times a week runs out every other Thursday.

Fix this by using real data. Pull your parts sales for the last 12 months. Sort by units sold, not by dollars. The top 50 parts by unit volume are your fast movers. Those need tight min/max control. The bottom 80% by volume can run lean or be ordered as needed.

Pick your lead time honestly

Lead time is the time from the moment you realize you need to reorder to the moment the part is on your shelf. Be honest with yourself.

• Stens via ground from a regional warehouse: 2 to 3 business days
• Rotary via ground: 2 to 4 business days
• Oregon: 3 to 5 business days
• OEM direct (Briggs, Kohler, Honda): 5 to 10 business days
• Stihl, Husqvarna OEM: 2 to 5 business days through dealer network

If you order weekly on Mondays, your effective lead time for a Tuesday stockout is 8 days, not 3. Plan for the worst case, not the average.

The seasonal overlay

A lawn mower shop does not have one inventory level per part. It has four, one for each season. Failing to account for this is the single biggest cause of springtime stockouts and wintertime cash-tied-up-in-inventory.

Multiply your baseline usage by these rough seasonal factors:

Part category	Spring (Mar-May)	Summer (Jun-Aug)	Fall (Sep-Nov)	Winter (Dec-Feb)
Mower blades	3.0x	1.5x	0.5x	0.2x
Air filters	2.5x	1.8x	0.6x	0.3x
Mower belts	2.0x	2.2x	0.7x	0.2x
Spark plugs	2.0x	1.5x	1.0x	0.5x
Snow blower shear pins	0.1x	0.1x	1.5x	3.0x
Snow blower belts	0.1x	0.1x	1.8x	2.5x
Carb kits (universal)	2.5x	2.0x	1.5x	1.0x

Run these in your head: if you sell 20 mower blades a week in June, you'll sell 40 in April. Your April min needs to be at least 2x your June min.

The 12 parts every small engine shop should stock deep

These are the parts that every shop runs through, regardless of region or specialty. If any of these are below 2 weeks of stock in-season, you have a problem.

• Universal fuel filter (in-line, 1/4")
• Briggs & Stratton air filter for Intek 190cc (most common residential)
• Kohler Courage 22 carb kit
• Tecumseh HSSK snow blower carb kit
• Toro 22" recycler blade (OEM part)
• Husqvarna deck belt for YTH series (2-cylinder 42")
• Stihl MS 250 air filter and bar nut assembly
• Kohler Command 20-25 oil filter
• Briggs/Tecumseh spark plug (Champion RJ19LM equivalent)
• 2-cycle premix oil (50:1 ratio, case of 24)
• Fuel line bulk (3/32" and 1/8" ID, 25 ft rolls)
• Universal starter rope (#4 1/2 size)

Build your depth around these 12. They are not the whole inventory. They are the anchor.

Example reorder points for a mid-size shop

Here's what realistic min/max levels look like for a shop doing roughly $800K in annual revenue, 2-3 techs, during peak season.

Part	Weekly usage	Lead time	Min	Max	Order qty
Briggs Intek air filter	12	3 days	10	40	30
Toro 22" blade	8	4 days	8	24	16
Tecumseh HSSK carb kit	3	5 days	4	12	8
Kohler Courage 22 carb kit	2	5 days	3	9	6
Universal fuel filter	15	2 days	10	50	40
50:1 premix quart	10	2 days	12	48	36
Stihl MS 250 air filter	4	4 days	4	16	12

These are starting points. Adjust monthly based on what actually sold. Your point of sale should show you this by week 2.

The counting routine that keeps it honest

Min/max levels only work if the numbers in the system match the numbers on the shelf. Physical counts drift. Techs pull parts and forget to scan. Customers pocket small items. Receive PO errors happen.

Do this:

1. Every part sold or used on a ticket gets scanned or manually decremented.
2. Every received part gets scanned against the PO before it goes on the shelf.
3. Cycle count 10 parts every morning before opening. Hit the full inventory every 30 days.
4. Anything with a variance over 10% between system and shelf gets investigated the same day.
5. Monthly, export usage data and re-tune min/max on the top 50 parts.

This takes 15 minutes a day. It saves $5,000 to $20,000 a year depending on your volume.

What to do next

Pull your last 12 months of parts sales tonight. Sort by unit volume. Identify the top 50. Set baseline min/max from real usage, apply the seasonal factor for the month you're in, and shelf-audit on Monday. You'll know within two weeks whether your lawn mower parts inventory is working for you or against you.