A Shopify app
Sell every size from one bottle, sack or drum.
Carboy keeps it as one pool, in ml or grams. Every size in Shopify follows. Carboy for decant shops
Carboy is in Shopify App Store review. Leave your email and we'll write the day it's approved. Free for one pool.
Tap a size to sell one
In sellers' own words
From 100+ seller threads on Shopify Community and other forums.
“If I sell both my 20ml it'll show that it's out of stock on 20ml, but in reality I still have 60ml left.”
Shopify Community, 2021 “We also need to track different products by volume. Meaning, we have 10 oz in stock and sell in quarter, half, and full ounces.”
Shopify Community, 2022 (opens in a new tab) “I am purchasing herbs by weight lets say 20 kg. And selling as one product with variations 10, 25, 50, 100,200, 500 and 1000 grams.”
Shopify Community, 2024 (opens in a new tab) “When we sell 15g sample bag x10, I have to adjust the inventory manually.”
Shopify Community, 2024 (opens in a new tab) “We have 50lb of Kenya roasted. this can be sold as 10 5lb bags or 66 12oz retail bags, or any combination of the two.”
Shopify Community, 2022 (opens in a new tab) “…the variant 50g will be out of stock, but the variant 10g will still be available, which is a major problem for my business…”
Shopify Community, 2024 (opens in a new tab) “…i recieve an order in Shopify for 5 litres of coconut oil … it's going down by only 1 and showing a stock of 99 litres.”
Shopify Community, 2024 (opens in a new tab) “The problem is that I have to set my inventory for each size. This causes a number of problems as its not a clear reflection of what I have in stock.”
r/shopify, 2026 (opens in a new tab) “We would like to add one large volume (our actual inventory) and then have these increment subtracted from the total inventory volume after each purchase.”
r/shopify, 2021 (opens in a new tab) “I'm having to constantly go in and manually update the availability. It's becoming quite frustrating for our front of house staff and for our cooks.”
Square Seller Community, 2020 (opens in a new tab)
“My challenge is inventory management. When someone orders, for example, 5 x 10ml decants, I need the system to automatically deduct 50ml from my main 100ml bottle stock.”
Shopify Community, 2024 (opens in a new tab) “We had a custom app built that managed to accomplish tracking inventory by volume but it only worked online, not at our POS.”
Shopify Community, 2022 (opens in a new tab) “…as things are starting to take off were starting to struggle with one main issue… stock control!”
Shopify Community, 2024 (opens in a new tab) “I've tried a number of stock sync or bundle apps to try to solve this but can't seem to get this to work.”
Shopify Community, 2023 (opens in a new tab) “I just want those variants tracked by how many TOTAL ounces I have available, not by how many ounces of each variant I have.”
Shopify Community, 2024 (opens in a new tab) “…if one product got sold 100kg, the quantity will reduce to 800kg of whole store and so on. And everything will be sold out once 900kg limit is reached.”
Shopify Community, 2025 (opens in a new tab) “…suppose a customer wants to purchase 1 pack but its out of stock in the inventory … But I still might have the 10 packs option in stock.”
Shopify Community, 2023 (opens in a new tab) “I sell ingredients in multiple sizes (1 oz, 2 oz, 4 oz, 8 oz, 16 oz), but all sizes pull from the same raw inventory (measured in ounces).”
r/shopify, 2026 (opens in a new tab) “…if I sell a lot of 250g bags from a shipment I have to adjust the 500g bags down to reflect that, making it a painful process.”
Square Seller Community, 2022 (opens in a new tab) “But if a variation (6kg for example) is purchased, only one will be removed from inventory. Is there a way to change that?”
WooCommerce forum, 2024 (opens in a new tab)
Every order moves the pool. Every size follows.
One bottle, one pool.
Bottle received+100.0 ml
An order takes 20 ml.
Order #104110 ml travel × 2−20.0 ml
Sixteen more orders.
#1042–10572 ml sample × 16−32.0 ml
A refund puts 10 ml back.
Refund #104110 ml travel × 1+10.0 ml
The 10 ml travel sells out.
#1058–106210 ml travel × 5−50.0 ml
A hand edit waits for you.
Edited in Shopify5 ml decant 1 → 4Held
More than the count
Reads variant names
- Sample / 2ml2 ml
- Decant - 5 ML5 ml
- 10ml Travel Spray10 ml
Sizes found3 of 3
Today's fill list
- 5 ml× 3
- 10 ml× 1
Total25.0 ml
Margin per size
5 ml decant$19.00
Margin30%
When it runs dry
Left60.0 ml
180.0 ml sold in 28 days
Runs dryin about 9 days
Built for the bad days
- Every order counts once
- Hand edits wait for you
- Checked every night
- Uninstalling drops nothing to zero
Pricing
Free
$0
1 pool
Starter
$12 / month
Up to 25 pools
Pro
$29 / month
Unlimited pools
Every feature on every plan.
Questions
What if a variant name has no size?
Carboy reads the size from each variant name: "Sample / 2ml", "10 ml Travel", "250g bag", "4 fl oz". If a name has none, you type it once, or leave that variant out of the pool, like a sealed full bottle.
What about hand edits in Shopify?
Carboy looks twice, a few minutes apart, in case an order is still on its way. If the change is still unexplained, it holds that size and asks you: add the change to the pool, or keep the pool. It never settles it on its own.
What if Shopify sends an order twice?
Every order counts once: Carboy remembers what it has already taken. And if Shopify never sends one, the nightly check at 03:00 your time picks it up and compares every size with the pool.
Can one pool feed several products?
Yes. A tea sack can feed a 50 g pouch product and a tasting set at the same time.
Can I sell in ounces and grams?
Yes. Carboy converts between ml, l, fl oz, g, kg, oz and lb inside the same pool.
Does it work with Etsy?
Not yet. Shopify comes first. If you need Etsy, write to us and say so; it decides what we build next.
What if I uninstall?
It stays exactly as Carboy last set it, so nothing drops to zero on the way out. We delete our copy of your pools 48 hours later.