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CO2 tank size selection is one of the first practical decisions in building a kegging setup, and getting it right saves both money and inconvenience over the long run. I’ve run both 5lb and 20lb tanks across years of kegging and the comparison has a clear practical winner for most homebrewers, though the right answer depends on your specific setup and usage patterns.
5lb vs. 20lb CO2 tank: capacity and usage
CO2 consumption in homebrewing kegging: A 5-gallon keg requires approximately 2–3oz of CO2 for force carbonation (pushing CO2 into solution at serving pressure over 1–2 weeks), plus approximately 0.5–1oz per gallon of beer dispensed (the CO2 used to push beer from keg to tap). Total CO2 per keg from force carbonation through complete dispensing: approximately 4–6oz for a 5-gallon keg. This means a 5lb (80oz) CO2 tank carbonates and dispenses approximately 13–20 five-gallon kegs before running out. A 20lb (320oz) tank provides proportionally 4× the capacity, approximately 50–80 five-gallon kegs. 5lb CO2 tank: The most common starter tank for homebrewing kegging. Compact (approximately 18″ tall, 5″ diameter) and fits inside a standard mini-fridge or kegerator. Relatively inexpensive to purchase ($30–50 new or $20–35 used). Refill cost: approximately $10–20 per fill at a welding supply or homebrew shop, the per-ounce CO2 cost is higher than a 20lb tank since exchange fees are often flat regardless of tank size. Aluminum 5lb tanks are significantly lighter than steel 20lb tanks, making them easier to transport for exchange. Frequency of exchange: for a homebrewer kegging 2–4 batches per month, a 5lb tank typically needs exchange every 4–8 weeks. 20lb CO2 tank: The preferred tank for serious homebrewers with multi-tap kegerators or high-volume brewing. Taller (approximately 27″ tall, 7″ diameter), does not fit inside a standard kegerator without modification; typically stored beside or behind the kegerator with the gas line passing through a drilled port. Refill cost: approximately $20–35 per fill at equivalent welding supplies, per-ounce CO2 cost is substantially lower than a 5lb tank since the fixed exchange fee is amortized over 4× more CO2. Frequency of exchange: every 4–6 months for a 2-tap homebrewer kegging 2 batches per month, eliminating most exchange trips. 10lb tank: A middle-ground option that fits some kegerators (approximately 22″ tall) and provides 2× the capacity of a 5lb at lower per-ounce cost. Worth considering for brewers who find the 5lb too small but can’t accommodate a 20lb externally.
Practical recommendation by setup
Choose 5lb when: Your kegerator is a mini-fridge or converted refrigerator with limited internal space and no external CO2 storage arrangement. You keg infrequently (1–2 batches per month) and the 4–8 week exchange interval is manageable. You’re new to kegging and want to start with lower initial investment. You transport the kegerator for events and need a light, portable CO2 tank. Choose 20lb when: You keg frequently (3+ batches per month) and the frequent exchange trips with a 5lb tank are an inconvenience. You have a dedicated kegerator with space beside or behind it for an external tank. You have multiple taps, the faster consumption of a multi-tap setup makes the 20lb’s higher capacity particularly valuable. You want to minimize the per-ounce CO2 cost over time. You’ve experienced running out of CO2 mid-carbonation or during an event and want a larger reserve buffer. Exchange vs. owned tank: Many gas suppliers offer tank exchange (swap empty for full) rather than refilling your specific tank. This is faster than waiting for a fill but means you may receive a tank of different age or condition. Owned-and-refilled tanks give more control over tank inspection and hydrostatic test date tracking. CO2 tanks require hydrostatic testing every 5 years, tanks with expired test dates will not be filled at most suppliers.
Common Questions
Where can I get CO2 tanks refilled for homebrewing?
CO2 tank refills for homebrewing are available from multiple source types with varying price, convenience, and service quality. Welding supply shops are typically the cheapest and most reliable source, they handle large volumes of industrial CO2 and fill homebrewing tanks as a minor side business. Pricing at welding supply shops is usually $15–25 for a 5lb fill and $20–35 for a 20lb fill. Homebrew shops offer CO2 fills as a convenience service but typically charge 20–50% more than welding suppliers for the same fill. Restaurant supply companies that service commercial draft beer systems are an option in some markets, they fill to food-grade CO2 specifications (the same grade required for beer). Beverage gas distributors (the companies that supply bars and restaurants with CO2) sometimes offer retail fill services. Fire extinguisher service companies fill CO2 tanks and are often overlooked, they work with the same aluminum tanks and can fill to homebrewing-grade CO2 specifications. Online and tank exchange: some homebrew shops participate in AirGas or similar exchange programs where you exchange an empty tank for a filled one. This is convenient but means you get a random tank rather than your own. For finding local sources: calling local welding supply shops (Air Liquide, AirGas, Praxair distributors, independent welding shops) is usually the best starting point. Homebrewing forums and club members in your area will typically have local recommendations for the cheapest and most convenient fills near you.
