What a trailer jack block does and why you need one
A trailer jack block is a sturdy platform that sits under your trailer's jack foot to keep it from sinking into soft ground, asphalt, or gravel when the trailer is parked. Without one, the jack foot can punch through the surface, tilt the trailer unevenly, or damage the ground beneath it. The block distributes the trailer's weight across a wider area so the jack stays stable and level.
You need a jack block whenever you park a loaded trailer for more than a few minutes — especially if you are on dirt, grass, gravel, or hot asphalt. Even concrete can crack under a concentrated load over time. A jack block is cheap insurance against a tilted trailer, a stuck jack, or damage you will have to pay to repair.
Key Takeaways
- A trailer jack block is a flat platform that prevents the jack foot from sinking into soft ground or damaging pavement.
- Blocks come in plastic, wood, or composite materials, with plastic and composite lasting longer in wet conditions.
- The block must be large enough to support the jack foot completely and thick enough not to compress under the trailer's weight.
- Place the block directly under the jack foot before lowering the jack, and remove it only after raising the jack fully.
- A block rated for your trailer's weight is more reliable than improvising with scrap wood or bricks.
Types of trailer jack blocks and what they cost
Plastic jack blocks are the most common choice. They are lightweight, do not rot or splinter, and cost between $15 and $40 per block depending on size and thickness. Most are 12 to 18 inches square and 2 to 4 inches thick. They handle repeated use well and work on any surface.
Wood blocks are cheaper upfront — often $5 to $15 — but they absorb water, rot over time, and can splinter or crack. If you use wood, pressure-treated lumber lasts longer than untreated, but even treated wood eventually fails in wet climates. Many people use wood as a temporary solution and upgrade to plastic later.
Composite blocks (made from recycled plastic and wood fiber) split the difference: they cost $25 to $50, resist rot and weather better than wood, and last as long as plastic. They are heavier than plastic, which some people prefer because the extra weight makes them less likely to shift.
Specialized jack blocks designed for specific trailer types — such as landing gear blocks for fifth wheels — cost more ($40 to $100) but fit the jack foot exactly and often have built-in features like angled surfaces for easier placement.
How to pick the right size and weight rating
The block must be large enough that the jack foot sits completely on top of it with at least 1 to 2 inches of clearance on all sides. A jack foot that hangs over the edge of the block defeats the purpose — the weight concentrates at the edge instead of spreading across the block. Measure your jack foot width and length, then choose a block at least 2 to 4 inches larger in each direction.
Thickness matters as much as width. A thin block will compress or crack under a heavy loaded trailer. Most jack blocks are 2 to 4 inches thick; use 4 inches if your trailer weighs more than 10,000 pounds or if you park on very soft ground. Check the manufacturer's weight rating — it should exceed your trailer's loaded weight by at least 20 percent.
If you tow a tandem-axle trailer or a fifth wheel, you may need two blocks — one under each jack foot or landing gear leg. Check your trailer's manual or the jack manufacturer's instructions to confirm. Some trailers have a single center jack that needs only one block; others have dual jacks that each need their own.
How to place and use a jack block correctly
Position the block on level ground directly under where the jack foot will land. If the ground is uneven, place the block on the high side so the jack foot will sit level. Lower the jack slowly until the foot rests fully on the block — do not let the foot rest on the edge or on the ground beside the block.
Once the jack is lowered onto the block, check that the trailer is level side to side. If it is tilted, raise the jack, adjust the block position, and lower again. A tilted trailer puts stress on the frame and makes it harder to hitch or unhitch. Spend the extra minute getting it level.
When you are ready to leave, raise the jack fully before moving the trailer. The jack foot must clear the block completely — if the foot catches the block edge as you pull forward, you can damage the jack or the block. Raise slowly and watch to confirm the foot clears. Only then move the trailer.
When not to use a jack block and what to do instead
You do not need a jack block if you are parked on solid concrete for just a few minutes — such as at a fuel stop or rest area. The risk of sinking is low, and the jack foot will not damage concrete in a short time. However, if you are staying more than an hour or parking on hot asphalt, use a block; hot asphalt can soften and let the jack foot sink.
If you do not have a block and cannot get one, do not use bricks, cinder blocks, or stacked wood scraps. These improvised solutions are unstable, can shift under the trailer, and may collapse suddenly. A collapsed jack can damage the trailer frame or injure someone nearby. If you are stranded without a block, park on the most solid surface available and use the jack only to level the trailer slightly — do not rely on it to hold the full weight for long.
In an emergency, a thick piece of plywood (at least 3/4 inch, ideally 1.5 inches) can work temporarily if you have nothing else. Lay it flat, center the jack foot on it, and monitor it closely. Replace it with a proper block as soon as you can.
Storing and maintaining your jack blocks
Store jack blocks in a dry place when not in use. Plastic blocks do not need maintenance, but wood blocks should be kept out of standing water and direct sun to slow rot. Composite blocks benefit from occasional rinsing to remove dirt and mold.
Inspect your blocks before each use. Look for cracks, deep gouges, or soft spots that suggest the material is breaking down. A cracked block can fail suddenly under load. If a block is damaged, replace it rather than risk it collapsing.
Keep your blocks with your trailer or towing gear so you always have them when you need them. Many people store a pair of blocks in a cargo box mounted on the trailer tongue or in the tow vehicle. This way you will not forget them or have to improvise.
Frequently Asked Questions
Can I use one block under a dual-jack trailer?
No. If your trailer has two jacks or landing gear legs, each one needs its own block. Using one block under both jacks will tilt the trailer and put uneven stress on the frame. Check your trailer manual to confirm how many jacks you have and how many blocks you need.
How thick does a jack block need to be?
Most trailers do well with 2 to 3 inches of thickness. If your trailer weighs more than 10,000 pounds loaded or you often park on soft ground, use 4 inches. Thicker is safer; thinner blocks can compress or crack under heavy weight.
Will a jack block work on gravel or dirt?
Yes, but the block itself may sink slightly into very soft ground. Place it on the firmest spot you can find, and consider using a thicker block (4 inches) if the ground is especially soft. The block still prevents the jack foot from punching through and getting stuck.
What if my jack foot is an odd shape?
Most jack feet are square or rectangular, and a standard block works fine. If your jack has an unusual shape — such as a wide base or angled foot — measure it carefully and look for a block designed for your trailer type. Specialized blocks for fifth wheels or specific brands are available and fit better than generic blocks.
Do I need to use a block on concrete?
Not for short stops, but use one if you are parked for several hours or on hot asphalt. Concrete is solid enough that the jack foot will not sink, but repeated use in the same spot can cause small cracks. Hot asphalt can soften under the concentrated weight, so a block is a good idea in warm weather.