What size anchor bolts do I need to bolt down a safe?

For a concrete slab, 1/2 inch wedge anchors are the common choice and 3/8 inch is the practical minimum. Match the carbide bit to the anchor diameter exactly — a 1/2 inch wedge anchor needs a 1/2 inch hole, not a 9/16 inch one — and drill about half an inch deeper than the embedment so debris has somewhere to go. On a wood floor, use 3/8 inch lag screws long enough to bite at least 1.5 inches into a joist, with a 1/4 inch pilot hole. Check the anchor manufacturer's own instructions for minimum embedment and installation torque; those figures vary between products.

Can you bolt a safe to a wood floor?

Yes, but into the joists rather than the subfloor. A 3/4 inch plywood subfloor on its own offers almost no pull-out resistance — a lag screw in plywood alone comes out with a pry bar and a few seconds of leverage. Locate the joists first with a stud finder or by measuring from a known joist, then use lag screws long enough to pass through the subfloor and still bite at least 1.5 inches of solid joist. If your safe holes do not line up with joists, bolt a length of 2x6 across two joists from below and anchor into that.

How deep should the hole be for a concrete anchor?

Deeper than the anchor's minimum embedment, by roughly half an inch, so dust and cuttings have somewhere to settle instead of stopping the anchor short. A typical residential garage slab is only about 4 inches thick, so keep total depth under about 3 inches and never drill through — you will hit the vapor barrier and gravel and the anchor will be worthless. Minimum embedment figures are printed on the anchor packaging and differ between wedge anchors, sleeve anchors and concrete screws. Follow the number on your box, not a general rule.

Do I need a hammer drill to bolt down a safe?

For concrete, yes. A standard drill with a masonry bit will polish a shallow crater in a slab and burn out the bit; the hammering action is what breaks the aggregate. A corded hammer drill or an SDS-plus rotary hammer is the right tool and both are widely available to rent for a day for less than the cost of a wasted afternoon. For a wood floor you only need a regular drill and a socket wrench, which is one reason wood-floor installations take about half the time.

Is it safe to drill into my garage slab?

Usually, but confirm what is in it first. Radiant floor heating tubing and post-tensioning cables both live inside slabs and cutting either is a serious, expensive problem — a severed post-tension tendon can release stored energy violently. Post-tensioned slabs are normally marked with a stamp or a placard near the garage door or on the foundation; if you see one, do not drill without professional scanning. Rebar is harmless to hit but will stop your bit: move over two or three inches and start a new hole. Keep anchors at least 4 inches from a slab edge or a control joint so the concrete does not spall.

How to Bolt Down a Safe: Concrete and Wood Floors

Written & researched by Priya Anand DIY & Tools Editor

Updated October 2026

Over-the-shoulder view of a person stacking plain unmarked storage bins on garage shelving, in soft early-morning light

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This is a 45-minute job on a concrete slab and about 20 minutes on a wood floor, at a materials cost of roughly $10 to $25. Difficulty is low — the drilling is the only real skill — but you need a hammer drill for concrete, and you need to know what is inside your slab before you make a hole in it. No permit is involved and no trade license is required. The one situation to stop and get professional help is a post-tensioned slab, which is marked and must not be drilled blind.

It is also the single most valuable thing you can do for a safe you already own. The typical residential loss is not a defeated lock; it is the whole safe leaving the house in the back of a vehicle and being opened somewhere quiet. A 70 lb keypad safe is a two-handed carry. Four anchors turn it into a fixture.

Dean Safe demonstrates bolting a gun safe down to a concrete floor

Tools and Materials

Hammer drill or SDS-plus rotary hammer — required for concrete. A standard drill will not cut a slab.
Carbide masonry bit matched to the anchor diameter — 1/2 in bit for a 1/2 in anchor, 3/8 in for 3/8 in. Not oversized.
Four wedge anchors, sleeve anchors or large-diameter concrete screws, 1/2 in preferred, 3/8 in minimum. Concrete screws are the most forgiving and can be removed.
Or, for a wood floor: four 3/8 in lag screws long enough to bite 1.5 in into a joist, plus 1/4 in pilot bit and washers.
Shop vacuum and a nylon hole brush — dust left in the hole is the number one cause of an anchor that never fully tightens.
Socket wrench, a torque wrench if you have one, safety glasses, hearing protection, an N95 mask — silica dust from concrete is not something to breathe.
Stud finder with live-AC detection for wood floors and for anchoring the back of a safe into studs.

If you have not bought the safe yet, buy one with pre-drilled base holes — nearly all do, and it saves you drilling hardened steel. Our home safe picks and gun safe picks both note which models ship with anchor hardware included.

Close-up detail of the material being worked in a storage & organization project, in bright midday sun

Before You Drill: What Is in the Slab

Three things can be inside a residential floor and two of them matter a great deal.

Post-tensioning cables. Found in some slab-on-grade homes, particularly in Texas, Arizona, Nevada, Florida and Colorado. The slab will normally carry a stamped warning or a placard near the garage door or on the foundation wall. Cutting a tendon releases stored tension and can be dangerous as well as structurally serious. If you see a post-tension marking, do not drill — have the slab scanned, or anchor the safe to a stud wall instead.
Radiant heating tubing. Increasingly common in basements and finished garages. If your floor is heated, get it scanned or pick a different location. There is no way to guess where the loops run.
Rebar or wire mesh. Harmless to hit and it will simply stop the bit. Move over two to three inches and drill a fresh hole. Do not try to drill through it.

Also check the practical geometry before you commit. A typical garage slab is about 4 inches thick, so your total hole depth needs to stay under roughly 3 inches. Keep every anchor at least 4 inches from a slab edge, a control joint or a visible crack — concrete near an edge spalls out when a wedge anchor expands, and an anchor in a crack holds nothing at all.

Bolting to a Concrete Slab: Step by Step

Position the safe and mark through the holes. Open the door and check clearance — a safe against a wall with the hinge side pinned is a safe whose door only opens 80 degrees. Leave at least a few inches of swing room. Mark each base hole with a masonry pencil or a nail set.
Move the safe out of the way. Do not drill under it. You need to see the holes, vacuum them and check depth, and you cannot do any of that with 200 lbs sitting on top.
Set the bit depth. Wrap a piece of tape around the bit at your target depth: the anchor's stated minimum embedment plus about 1/2 in. Read the number on the anchor box — it differs between wedge anchors, sleeve anchors and concrete screws, and the packaging is authoritative for the product in your hand.
Drill each hole square to the floor. Start slowly to keep the bit from wandering, then apply steady pressure. Do not lever the drill; let the hammering do the work. If the bit stops advancing, you have found rebar — relocate.
Clean the holes properly. Vacuum, brush with a nylon hole brush, vacuum again. This step is skipped more than any other and it is the reason anchors spin without tightening. Dust acts as a lubricant between the anchor and the concrete.
Reposition the safe over the holes. Have help. Line up all four before you drop it fully, because shuffling a loaded safe across fresh holes chips the edges.
Insert the anchors. For wedge anchors, fit the washer and nut so the nut is flush with the top of the threads, then drive the anchor through the safe base into the hole with a hammer until the washer sits against the steel. For concrete screws, drive them with a socket and an impact driver on a moderate setting.
Tighten to the anchor manufacturer's stated installation torque. This is a real number on the packaging, not a matter of feel. Over-torquing a wedge anchor strips the cone out of the concrete and the anchor becomes decorative; under-torquing never sets the wedge. If you have no torque wrench, tighten firmly and then a quarter turn more, and re-check in a week.
Check the door. Open and close it fully. A safe pulled down onto an uneven slab can rack its frame slightly and bind the bolt work. If the door has become stiff, back the anchors off, shim the low corner with a steel washer stack, and re-tighten.

Three-quarter view of a person stacking plain unmarked storage bins on garage shelving, in soft overcast light

Bolting to a Wood Floor

Faster and needs no hammer drill, but the joists do all the work.

Find the joists. A stud finder works through most floor coverings; failing that, measure from a known joist location in a basement or crawl space. Residential joists are usually at 16 in centers, occasionally 24 in.
Position the safe so at least two base holes land over joists. Two good anchors into solid framing beat four into plywood. If nothing lines up, screw a 2x6 across two joists from below and lag into that.
Drill pilot holes. A 1/4 in pilot for a 3/8 in lag screw in softwood framing. Drill through the subfloor and into the joist to the depth of the lag, less about half an inch.
Drive the lag screws with washers. Use a socket wrench rather than an impact driver for the last turns so you can feel the head seat. Stop when the washer is firm against the steel — keep going and you will strip the threads out of the wood, which is not recoverable in the same hole.
Verify you have real penetration. A 3/8 in lag through 3/4 in plywood needs to be at least 2.5 in long to get 1.5 in of joist. Measure rather than assume.

The Mistakes That Leave an Anchor Loose

Mistake	What happens	Fix
Hole not cleaned	Anchor spins, never reaches torque	Vacuum, brush, vacuum. Every hole.
Oversized bit	Wedge anchor cannot grip; pulls out under load	Bit diameter must equal anchor diameter
Hole too shallow	Anchor bottoms out and lifts the safe as you tighten	Drill embedment plus 1/2 in; tape-mark the bit
Anchor near an edge or joint	Concrete spalls out in a cone; zero holding	Stay 4 in from edges, joints and cracks
Lag into plywood only	Pulls out with modest leverage	Hit a joist, or add blocking below
Over-torqued wedge anchor	Cone strips; anchor feels tight but holds nothing	Use the stated installation torque
Drilling under the safe	Cannot clean or measure the hole	Mark, move the safe, drill, clean, reposition

Wide environmental view of a person stacking plain unmarked storage bins on garage shelving, in soft overcast light

If You Rent, or Cannot Drill

Drilling a slab or a floor in a rental usually needs the landlord's consent, and a heated or post-tensioned floor rules it out regardless. The alternatives are less good but not useless:

Anchor the back into studs. Many safes have rear holes. Two 3/8 in lag screws into a stud through drywall is a meaningful improvement over nothing, and the holes patch easily.
Bolt the safe to something heavy. A loaded steel shelving unit anchored to a wall, or a workbench bolted to studs, makes a small safe far harder to remove. Our guide to anchoring shelves into studs and concrete covers the fastener choices for that.
Hide it well. Concealment is a real security mechanism and it costs nothing — see where to hide a safe in a house.
Consider an in-wall unit instead. It attaches to framing rather than to a floor, and the flange screws into two studs. Our wall safe picks explain the trade-offs, including the shallow depth limit.

Safety and Silica

Cutting concrete produces respirable crystalline silica, which is a recognized occupational lung hazard rather than ordinary nuisance dust. For four holes in a garage the exposure is brief, but wear an N95 or better, use a vacuum at the hole, and ventilate. Wear eye protection — hammer drilling throws chips — and hearing protection, because an SDS hammer in an enclosed garage is genuinely loud.

Get help lifting. A 200 lb safe positioned by one person is how backs and fingers get hurt, and a dropped safe on a slab damages both. Use an appliance dolly and straps if the safe is heavy, and never tilt a tall safe with the door unlatched.

After the Install

Two small habits finish the job. Re-check the anchor torque after a week or two — settling and the initial seating of a wedge cone can leave a nut a quarter turn loose, and this is the only maintenance an anchored safe ever needs. And keep the override key somewhere other than the room the safe is in. An anchored safe with a dead keypad battery and the key locked inside it is a locksmith call, and it is a much more likely outcome than a burglary.

If your safe is fire rated, put the contents in a sealed pouch inside it as well. Fires are extinguished with water, and documents that survive the heat are routinely ruined by the hose — fireproof document bags cover that layer, and are fireproof safes actually fireproof? explains what a fire rating does and does not buy you.

How to Bolt Down a Safe (Concrete Slab and Wood Floor)