How Many Amps for a Garage Workshop? 100-Amp Rule
A garage workshop often needs a workshop supply of around a 100-amp subpanel, but about 60 amps can work for light-duty tools, and about 200 amps is commonly considered better for a heavier garage workshop with saws, dust collection, and electric heat. This guide separates whole-workshop supply sizing from individual branch circuits: the room may need 60A, 100A, or 200A capacity overall, while the tools inside it may still use 15A or 20A branch circuits. If the supply is undersized, breakers trip, simultaneous use gets limited, and rewiring may be needed later. This guide covers breaker capacity, circuit count, and winter loads by tool mix.
Understanding circuit ratings and motor loads
The amp rating tells you how much current a circuit can carry before the breaker opens. That matters in a garage because tools rarely run alone; lights, chargers, a dust collector, and a heater can all share the same supply if you plan it that way.
One tool’s nameplate is only the starting point. A workshop that looks modest on paper can trip breakers once a saw starts up and a compressor kicks on a few seconds later.
What the amp rating tells you
On a typical 120V household circuit, the common branch-circuit sizes are 15A and 20A. Electrical code guidance in this article uses a practical ceiling of 80% of the circuit rating for continuous loads, so a 15A circuit should stay below about 12A for continuous use.
That limit matters because a motor load can run near its rating and still leave little headroom for anything else. If the circuit also feeds lights or a charger, there is less margin left for startup surge.
Why one tool rating is not enough
A garage workshop is a system, not a single machine. A table saw may run within its rating, but adding dust collection and a space heater can push the branch circuit into overload territory even if each item seems reasonable by itself.
That is why planning by room load works better than planning by one tool. You are sizing for the moments when several things come on together.
When winter loads change the answer
Winter changes the electrical picture because heaters add steady draw, and cold motors can be less forgiving at startup. A circuit that works in summer may nuisance-trip once a portable heater and a compressor share the same branch.
A common first-timer mistake is to size the workshop for the saw alone. Then a heater gets plugged in, the compressor starts, and the breaker trips during a cut.
How many amps do you really need?
Most garage workshops need more than one circuit if you want to run tools with some flexibility. A single 15A branch circuit is fine for a very light setup, but a 20A circuit is the more practical baseline for many portable tools, and 240V becomes the better answer for larger stationary equipment.
That is the room-level supply; the individual tools inside it still need the correct branch circuits.
If you truly use one tool at a time and keep the rest of the load small, a 15A circuit can work for a light-duty garage shop. If you want overlap between a tool and a compressor, or a tool and a heater, 20A or a separate circuit is the safer planning choice.
Shared use is where many garage workshops run out of headroom. The breaker does not care that the saw is the main load if the compressor starts while the saw is already pulling current.
15A, 20A, and 240V in plain terms
A 15A circuit is common, but it often falls short for multiple shop tools or any setup that includes a heater, compressor, or dust collection. A 20A circuit is the common target for many portable shop tools and often uses 12 AWG wire when installed to code.
A 240V circuit makes sense for larger stationary equipment because it can cut current for the same power level. That lower current helps with voltage drop and leaves more room for the rest of the shop.
A simple rule for sizing the room
If the workshop is light-duty, start with one 20A general-purpose tool circuit plus lighting. If you plan to run a compressor, dust collector, or heater at the same time as a saw, add dedicated circuits or move the biggest loads to 240V.
For a more capable garage shop, two or more dedicated 20A circuits are often a better minimum than one oversized general circuit. The point is not to chase a single amp number; it is to keep the room usable when tools overlap.
120V vs 240V circuits
A 120V household circuit is the normal garage-shop starting point. It handles many portable tools well, but once the motor size rises or the duty cycle gets longer, 240V is often the better fit.
Voltage matters because power can be delivered with less current at higher voltage. Lower current means less stress on the circuit and less chance of nuisance trips.
What a 120V household circuit can handle
On 120V, the practical range for many home-shop tools is 15A or 20A. That covers lights, chargers, benchtop tools, and many portable saws, but it does not leave much spare capacity once a motor starts and other loads are already on.
A 120V circuit is also where extension cords matter most. Long cords and undersized wire can lower voltage at the tool, which can make motors run harder.
When a 240V branch circuit makes sense
A 240V circuit suits larger fixed equipment. Cabinet table saws are often designed for 240 volts, and that setup is usually a better match for a dedicated branch circuit than for a shared 120V outlet.
If your shop plan includes heavy saws, dust collection, or electric heat, 240V can be the cleaner answer for at least one of those loads. It keeps the high-demand equipment off the general-purpose circuit.
Why voltage changes current draw
For the same output, higher voltage means lower current. That is why a machine that would strain a 120V branch may work more comfortably on a 240V circuit with the proper breaker and wiring.
It also explains why a 240V upgrade is often about reliability as much as capacity. Lower current reduces voltage drop and helps avoid the slow, annoying trips that show up when a shop is busy.
Common tool amp ranges
Tool amperage varies by type, size, and voltage. The useful question is not only how many amps the tool needs, but how much startup surge it creates and whether anything else will share the same circuit.
Table saws
Benchtop or portable table saws are commonly rated at 10-15 amps. Contractor table saws are generally 13-15 amps at 120 volts. Cabinet table saws are often designed for 240 volts.
A 13-15A 120V table saw is a strong candidate for a dedicated 20A circuit. That leaves room for startup surge and keeps the saw from competing with another load on the same branch.
Small air compressors
A small air compressor typically uses between 7 to 15 amps. Some portable small compressors might reach 20 amps. Starting amps can be 2-3 times higher than running amps, so a marginal circuit can trip the moment the tank pressure drops and the motor restarts.
That makes compressors one of the most common nuisance-trip sources in a garage workshop. They often cycle at inconvenient times, which is exactly when the saw or dust collector is already in use.
MIG welders and other high-draw tools
MIG welders can run on either 120V or 240V depending on output, so the circuit must match the machine’s rated input and duty cycle. Higher-output welders belong on their own properly sized branch circuit, especially if the workshop also runs woodworking tools.
Other high-draw equipment, such as dust collectors and large heaters, belongs in the same planning bucket. They may not all have the same nameplate current, but they all reduce the margin available to the rest of the shop.
Starter surge and nuisance trips
Starting amps matter because motors briefly pull more current at startup than they do while running. Starting amps can be 2-3 times higher than running amps, which is often enough to trip a breaker that looked adequate on paper.
That surge is the hidden reason a garage workshop can seem fine until the first cold morning or the first time two machines start close together.
Running amps vs starting amps
Running amps are the draw once the motor is up to speed. Starting amps, or inrush current, are the brief spike at startup. The brief spike is what trips many workshop circuits, especially when the breaker is already close to its limit.
A table saw’s startup surge may briefly reach 25-35A for a 15A saw. That does not mean the saw needs a 35A breaker; it means the circuit must tolerate a short surge without being overloaded by everything else on the branch.
Which tools are most likely to trip breakers?
Tools with motors are the main culprits: table saws, compressors, dust collectors, and some larger shop vacuums. Compressors can be especially troublesome because they restart automatically, often without warning.
Heaters add a different problem. They do not surge like a motor, but they consume a steady share of the circuit, which leaves less headroom for the next startup event.
Why winter use raises the risk
Cold weather raises the odds of a trip because the heater is already using part of the circuit and motors may need a harder start. Add a compressor cycling in a colder garage, and the margin gets thin quickly.
Suppose your saw runs on a shared 20A branch with a compressor. In summer, the setup may seem acceptable. In winter, the same branch can trip as soon as the compressor kicks in during a cut.
Garage circuit plan table
This table translates common shop tools into a practical branch-circuit plan. The “share” column assumes normal workshop use, not an empty garage with nothing else plugged in.
| Common tool or load | Running amps | Likely starting surge | Recommended circuit size | Can safely share a branch circuit? |
|---|---|---|---|---|
| Portable table saw | 10-15A | 25-35A for a 15A saw | Dedicated 20A, 120V | Usually no with a compressor or heater |
| Contractor table saw | 13-15A | High enough to nuisance-trip a marginal branch | Dedicated 20A, 120V | No, if you want reliable cutting |
| Cabinet table saw | 12-18A | Lower current at 240V, but still a motor surge | Dedicated 240V circuit | No with general garage loads |
| Small air compressor | 7-15A | 2-3 times running amps | Dedicated 20A if portable unit approaches 20A | Only with very light loads nearby |
| MIG welder, 120V model | Varies by output | Depends on machine and duty cycle | Match the rated input circuit | Generally no with other shop tools |
| MIG welder, 240V model | Varies by output | Depends on machine and duty cycle | Dedicated 240V circuit | No |
| Lighting and battery chargers | Low | Small | Can share a general circuit | Yes, if the circuit is not loaded by tools |
| Portable heater | High and steady | None or small | Dedicated circuit if possible | No with saws or compressors |
Circuit and cord sizing
Breaker choice and wire size have to match. A 20A breaker is a common target for many portable shop tools, and 12 AWG wire is typically used on many code-compliant 20A branch circuits.
For extension cords, 12 AWG is the relevant size for many 13-15A tools, and 10 AWG is the better choice when the run is longer or the load is heavier. The goal is to reduce voltage drop before it starts affecting the motor.
15A vs 20A breaker choices
A 15A circuit is common, but it often falls short once the workshop includes a saw plus anything else. A 20A circuit gives more usable headroom and is a better target for most portable shop tools.
That does not mean every outlet in the garage should be 20A by default. It means the tool circuit should be planned as a tool circuit, not treated like a general spare outlet.
12 AWG and 10 AWG extension cords
The article’s tool guidance pairs 13-15A tools with 12 AWG extension cord wire. That is a practical starting point for avoiding excess voltage drop on normal garage runs.
Use 10 AWG when the cord is longer, the load is heavier, or the tool is sensitive to low voltage. A bigger cord does not create more power, but it can help the tool get the voltage it needs.
When to stop using a long cord
If a tool slows down, labors on startup, or trips more often when a cord is added, the cord may be part of the problem. Long, undersized cords create voltage drop and make the circuit behave as if it were smaller than it really is.
A dedicated receptacle is the cleaner answer for a fixed tool. If the cord is only there because the outlet is far away, the wiring plan may need to be changed instead of the cord.
Can you run tools on one circuit?
Sometimes, but only for light combinations. A table saw and compressor can share one circuit on paper, yet in real use the compressor’s startup surge can trip the breaker while the saw is already drawing current. Add a heater, and the odds get worse.
For a garage workshop, one shared circuit is usually acceptable only for lighting, chargers, and very light intermittent loads. Most productive shops need at least one dedicated tool circuit, and many need two or more.
Table saw plus compressor
Can I run a table saw and compressor on one circuit? Usually not if you want consistent results. A 13-15A saw and a compressor that can pull 7-15A leave too little margin for startup surge on a 15A or even a busy 20A branch.
If both tools are in frequent use, separate them. The saw gets a dedicated circuit, and the compressor gets its own branch or a 240V upgrade if the machine calls for it.
Saw plus heater or dust collector
A saw plus heater is a poor combination on one branch circuit. A saw plus dust collection can be workable only if the dust collector is small and the circuit has enough reserve, which is uncommon in a fully used garage shop.
Heating loads are especially troublesome in winter because they consume current continuously. That leaves less room for the next motor start.
When a dedicated circuit is the safer answer
A dedicated circuit reduces nuisance tripping and keeps other loads off the branch circuit. It is the safer choice for high-draw tools, and it is the simplest way to protect a workshop from accidental overloads.
If a machine has a specific input requirement, follow that requirement rather than guessing. The nameplate or owner’s manual should drive the circuit size, not the receptacle that happens to be available.
For a light garage workshop, 20A on one or two circuits may be enough if you are mostly running portable tools one at a time. For a more serious shop with a table saw, compressor, dust collection, and winter heat, a larger electrical plan is needed, often with dedicated 20A circuits and at least one 240V branch for heavy equipment.
The practical answer is that the workshop needs enough amperage for simultaneous use, not just for the largest single tool. That is why a circuit count matters as much as the total supply size.
Frequently asked questions
How many amps for a garage?
A garage can be wired with very different amp totals depending on use. A basic garage may work with a modest set of general-purpose circuits, while a workshop with saws, compressors, and heat needs a bigger plan.
Do I need a 20 amp circuit for a workshop?
For many home woodworkers, yes. A 20A circuit is the common target for portable shop tools and gives more usable headroom than a 15A branch. It is especially useful if you want to avoid nuisance trips from motor startup or light shared loads.
How many amps does a garage workshop need for power tools?
Power tools alone may fit on a pair of 20A circuits if the tools are used one at a time. Once you add a compressor, heater, or dust collection, the workshop usually needs more than that. The answer depends on overlap, not only on tool count.
What size breaker do I need for a garage workshop?
For many portable tools, a 20A breaker is the practical choice, with 12 AWG wire in many code-compliant installs. Larger cabinet saws and bigger equipment often call for 240V branch circuits with dedicated wiring and the breaker size specified by the machine’s nameplate.
How many amps does a small air compressor use?
A small air compressor typically uses between 7 to 15 amps, and some portable small compressors might reach 20 amps. Starting amps can be 2-3 times higher than running amps, so a circuit that seems adequate on paper may still trip during restart.
How many amps does a table saw use in a home shop?
Benchtop or portable table saws are commonly rated at 10-15 amps, and contractor table saws are generally 13-15 amps at 120 volts. Cabinet table saws are often designed for 240 volts. A 13-15A 120V saw is usually best on a dedicated 20A circuit.
What amp circuit do garage tools usually need?
The common answer is not one circuit size for everything, but a mix: one or more 20A branches for portable tools and dedicated circuits for larger equipment.
Is 15 amps enough for a garage workshop?
It can be enough for a very light workshop with one tool at a time and minimal extra load. It is often not enough once you add a table saw, compressor, heater, or dust collection. A 15A branch is common, but it is not a strong all-purpose shop answer.
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