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Instant Concrete Calculator
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Recommended Tools
- 2x4 or 2x6 Lumber (Forms)
- Wooden Stakes
- Duplex Nails
- Gravel / Road Base
- Rebar or Wire Mesh
- Screed Board
- Bull Float
- Edger & Groover
Why Professionals Use This Tool
Built for speed and compliance with industry estimation standards.
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Formulas aligned with American Concrete Institute guidelines.
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10% safety margin included for subgrade variation.
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Need Professional Help?
Instant Concrete Calculator helps you plan, but large projects often need a pro.
Knowledge Base
Professional concrete advice, from planning to maintenance.
First-Time DIY Guide
Can I really do this myself?
Yes, with preparation and a helper.
Concrete waits for no one, but it is not magic. The secret is preparation. Have all your tools rented and ready the day before. Do not attempt a large patio (over 10x10) alone—get at least two strong friends. One person mixes/pours, one screeds/finishes. Start small (like a generator pad or trash can slab) to get the feel of the material before tackling a driveway.
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What tools do I absolutely need?
Screed board, bull float, hand float, edger, broom.
Don't improvise tools. You need: 1. A straight 2x4 for screeding. 2. A bull float (rent this!) to smooth the wet concrete. 3. A magnesium hand float for bringing up cream. 4. An edging tool for rounded corners. 5. A finishing broom for texture. 6. Rubber boots and gloves (concrete burns skin!).
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Planning & Prep
Why is the subgrade so important?
Your slab is only as strong as the ground under it.
Concrete is heavy. If you pour on soft grass or loose dirt, the slab will sink and snap. You MUST remove all organic material (grass/roots). Put down 4 inches of gravel (crushed stone) and COMPACT it with a plate compactor until it is rock hard. If you walk on it and leave footprints, it is not ready.
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Should I wet the ground before pouring?
Yes, dampen the subgrade.
If you pour wet concrete onto bone-dry dirt or gravel, the ground will suck the water out of the concrete too fast, causing cracks. Spray the gravel lightly with a hose just before the truck arrives (no puddles, just damp).
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Mixing Methods
Tips for mixing concrete bags
Rent a mixer; measure your water.
Mixing 40 bags in a wheelbarrow is back-breaking and too slow for a good finish. Rent a tow-behind mixer or a portable electric mixer. measure the water for the first batch exactly according to the bag. Count your bags before you start—running out halfway is a nightmare.
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What is a "Dry Pour" and should I do it?
Not recommended for long-term durability.
The "dry pour" trend (dumping dry bags and misting with water) is popular on social media but risky. Without mechanical mixing, the center of the slab often remains dry powder or weak, crumbly concrete. It has no structural integrity and will likely crumble after a few freeze/thaw cycles. It is fine for a mailbox post, but bad for a patio.
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Reinforcement
Rebar 101: Size and Placement
#3 or #4 bar on chairs.
Rebar (steel reinforcement) keeps concrete together when it cracks. Use #3 (3/8") or #4 (1/2") bars. Lay them in a grid (checkerboard) spaced 16 or 24 inches apart. Tie them together with wire ties. CRITICAL: Use "chairs" to hold the rebar up 2 inches off the ground. Rebar lying on the dirt does nothing.
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Wire Mesh: Rolls vs. Sheets
Flat sheets are better; pull it up as you pour.
Wire mesh is cheaper than rebar but harder to use. It comes in rolls (which curl up and are a nightmare) or flat sheets (recommended). If you don't use chairs, you must "hook" the mesh and pull it up into the middle of the wet concrete as you pour, or it will stay on the bottom and be useless.
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Does Fiber replace Rebar?
No. Fiber is for surface cracks; Rebar is for structure.
Fiber mesh looks like hair mixed into the concrete. It is amazing for preventing those tiny spiderweb cracks on the surface. However, it does not stop the slab from snapping in half if the ground settles. For the best slab, use BOTH rebar (for strength) and fiber (for surface durability).
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The Pour & Finish
Step 1: Screeding (Striking Off)
Leveling the wet mud.
As soon as you pour, use a straight 2x4 board resting on your forms. Saw it back and forth while pulling it down the length of the pour. This fills the voids and levels the surface. Have a helper rake the excess concrete away from the board as you pull.
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Step 2: The Bull Float
Push away flat, lift front edge to pull back.
Immediately after screeding, run the bull float (the big long tool on a pole) across the slab. This pushes down rocks and brings up the "cream" (smooth paste). TIP: When pushing away, lift the BACK edge slightly so it doesn't dig in. When pulling back, lift the FRONT edge.
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Step 3: The Waiting Game (Bleed Water)
Do NOT touch it while it's shiny!
After bull floating, water will rise to the surface. This is "bleed water." DO NOT finish the concrete while this water is sitting there. If you trowel the water back in, the top layer will be weak and dusty forever. Wait for the water to evaporate and the sheen to leave.
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Step 4: Edging
Create a durable rounded corner.
Once the bleed water is gone and the concrete is firming up, run your edging tool between the concrete and the form. This creates a nice radius and prevents the edges from chipping off later.
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Step 5: Floating & Troweling
Float, Trowel, then Broom. Watch the bleed water!
Use a Magnesium (Mag) float to smooth out the bull float marks. You can use a steel trowel to tighten the surface for a cleaner finish before brooming, but do NOT trowel too early! Steel trowels seal the surface—if you do this while bleed water is present, you will trap the water underneath and cause the surface to flake off later.
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Step 6: Broom Finishing
Texture for safety.
For outdoor slabs, drag a concrete broom gently across the surface once it is hard enough to hold a fingerprint but soft enough to scratch. This creates grooves for traction. If the broom is pulling up chunks of rocks, it's too wet—wait 15 minutes.
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Post-Pour & Maintenance
Control Joints: Wet vs. Saw Cut
Cut it before it cracks itself.
Concrete WILL crack. You choose where. You can use a "groover" tool while the concrete is wet to make lines, OR you can wait 24 hours and use a saw with a diamond blade. The cut must be at least 1/4 the depth of the slab (1 inch deep for a 4-inch slab). Place joints every 8-10 feet.
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When and why to seal?
Seal after 28 days for protection.
Sealer protects concrete from oil stains, salt, and water absorption. "Cure and Seal" can be applied immediately, but high-quality penetrating sealers should be applied after the concrete is fully cured (28 days). Re-seal every 2-3 years to keep it looking new.
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Winter Warning: No Salt!
Salt destroys new concrete.
During the first winter, your concrete is still curing internally. DO NOT use de-icing salt (sodium chloride) or even "safe" melts. They cause freeze-thaw cycles that pop the surface off (spalling). Use sand for traction instead.
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