16x20 Concrete Slab Concrete Calculator
With 320 square feet of surface area, a 16x20 slab is the standard minimum size for a functional single-car garage or spacious residential patio. At this scale, concrete volume exceeds 4 cubic yards, making ready-mix batch truck delivery mandatory.
Custom 16x20 Concrete Slab Interactive Calculator
Pre-populated with 20 ft × 16 ft. Adjust thickness or unit system below for immediate real-time calculations.
Raw volume estimate. Standard practice is to add 5%–10% extra for form deflection, spillage, and uneven subgrade.
Rebar Grid & Control Joint Visualizer
Real-time scaled layout calibrated to ACI 318 structural concrete standards.
Ground Excavation & Gravel Subbase
Concrete flatwork requires excavating native soil to accommodate both the compacted gravel base and slab thickness.
Call-a-Batch-Plant Order Cheat Sheet
Concrete dispatchers move fast. Have these exact technical answers ready when placing your ready-mix delivery call.
Includes +10% waste buffer. Plants meter in 1/4-yard increments.
Air-entrained exterior flatwork mix (freeze-thaw & vehicle rated).
Standard workability for direct chute pours. If using a line pump, specify 3/8" pea gravel mix.
Suppliers typically include 5–7 mins/yard free unloading. Additional truck standby costs ~$2.50–$3.50/minute.
1. Project Dimensions & Area Specifications
| Length | Width | Thickness | Surface Area |
|---|---|---|---|
| 10.0 ft | 10.0 ft | 4.0 in | 100 sq ft (9.3 m²) |
2. Concrete Volume & Batch Order Requirements
| Net Calculated Volume | Recommended Order (+10% Waste) | 80-lb Pre-Mix Bags | 60-lb Pre-Mix Bags |
|---|---|---|---|
| 1.23 cu yds 33.3 cu ft / 0.94 m³ | 1.35 cu yds Ready-Mix Batch Plant Order | 56 bags | 74 bags |
3. Steel Reinforcement & Crack-Control Joint Schedule
| Rebar Specification | Grid Spacing | Bar Count | Linear Footage | Total Steel Weight | Control Saw Cuts |
|---|---|---|---|---|---|
| #4 Rebar (1/2" dia) | 18" On-Center | 14 total (7L + 7T) | 146 lin ft | ~98 lbs (+10% lap) | 0 cuts (max 10' spc, 1.0" deep) |
4. Jobsite Material Checklist
How It Is Calculated
For a slab measuring 10 ft long × 10 ft wide × 4 in thick:
- Normalize Dimensions to Canonical Base Unit (Meters)
Convert length, width, and thickness to meters using exact NIST international conversion factors.
Length: 20 ft = 6.096 m | Width: 16 ft = 4.8768 m | Thickness: 4 in = 0.1016 m→ 6.096 m × 4.8768 m × 0.1016 m - Calculate Volume in Cubic Meters
Multiply normalized length by width by thickness.
6.096 × 4.8768 × 0.1016→ 3.02046363648 m³ - Convert Volume to Cubic Feet
Convert cubic meters to cubic feet using exact factor (1 cu ft = 0.028316846592 m³).
3.02046363648 / 0.028316846592→ 106.66666666666667 cu ft - Convert Volume to Cubic Yards
Convert cubic feet to cubic yards (27 cu ft = 1 cu yd).
106.66666666666667 / 27→ 3.9506172839506175 cu yd
Concrete Volume & Bag Requirements by Depth
Concrete slabs are poured at different depths depending on intended vehicle or structural weight. The table below compares raw volume against recommended order volume (+10% safety buffer for uneven subgrade and form deflection).
| Thickness | Common Applications | Exact Yards | Order Yards (+10%) | 80 lb Bags | 60 lb Bags | Ready-Mix Logistics |
|---|---|---|---|---|---|---|
| 4″ | Standard Patio / Shed / Sidewalk | 3.95 yd³ | 4.35 yd³ | 196 | 261 | 1 truckload (43% of 10-yd mixer) |
| 5″ | Residential Garage / Light Truck Pad | 4.94 yd³ | 5.43 yd³ | 245 | 326 | 1 truckload (54% of 10-yd mixer) |
| 6″ | Heavy Equipment / Commercial / RV Pad | 5.93 yd³ | 6.52 yd³ | 294 | 392 | 1 truckload (65% of 10-yd mixer) |
Ideal Projects for a 16x20 Concrete Slab
- Small single-car detached garage or carriage house floor
- Large covered backyard entertaining patio with outdoor kitchen
- Workshop, art studio, or home gym detached accessory building
- Double golf cart or utility vehicle storage shed
Gravel Subbase & Ground Prep Specifications
A durable concrete slab requires a solid, well-draining foundation to prevent settlement cracking and frost heave:
Compacted in 2-inch lifts with a mechanical plate compactor to 95% standard Proctor density. Use our dedicated Gravel & Subbase Material Calculator to estimate base depth for different soil types.
Reinforcement Schedule (#4 Rebar Grid)
Tensile reinforcement resists bending stresses from temperature fluctuations and heavy localized point loads:
Support rebar on approximately 54 concrete dobies or plastic rebar chairs to maintain reinforcement in the middle third of the slab. Alternatively, you may install 6x6 – W1.4/W1.4 welded wire reinforcement sheets (with 6" lap allowance). View our Concrete Rebar & Mesh Calculator for comprehensive cut lists.
Contraction Joint Layout (Crack Prevention)
Concrete inevitably shrinks as water evaporates during curing. Control joints create intentional weakened planes that dictate where microscopic hairline cracks occur, keeping them straight and unnoticeable:
Reference: ACI 302.1R Guide for Concrete Floor and Slab Construction recommends maximum joint spacing in feet equal to 2 to 2.5 times slab thickness in inches.
Estimated Cost for a 16x20 Concrete Slab
Covers ready-mix concrete delivery, gravel base, #4 rebar, lumber formwork, and stakes.
Includes excavation, subgrade prep, gravel compaction, rebar placement, pour, screeding, and professional broom/trowel finish.
DIY materials (ready-mix concrete, gravel base, #4 rebar, forms, vapor barrier) average $1,400 to $2,200. Professional installation typically costs $8 to $13 per sq ft ($2,560 to $4,160). For detailed budget modeling including regional truck delivery fees and pump rentals, use our Concrete Cost & Budget Estimator.
Frequently Asked Questions: 16x20 Concrete Slab
How many cubic yards of concrete are in a 16x20 slab?
At 4 inches thick, a 16x20 slab requires 3.95 cubic yards of concrete (4.35 cubic yards with a 10% safety margin). If poured at 5 inches for a garage floor, you will need 4.94 cubic yards (5.43 cubic yards with 10% waste). At 6 inches, order 6.52 cubic yards.
How many tons of gravel base do I need for a 16x20 slab?
A 4-inch compacted subbase under a 16x20 slab requires 3.95 cubic yards of crushed #57 stone or road base. At a compacted density of 1.4 tons per cubic yard, order approximately 5.5 to 6.0 tons of gravel.
How many sticks of rebar for a 16x20 slab?
With #4 rebar spaced at 18 inches on center, you need 11 bars running along the 20-foot length and 14 bars along the 16-foot width. Accounting for edge setbacks and 10% lap splices, this totals 489 linear feet, which equals twenty-five 20-foot rebar sticks.
Explore Other Popular Concrete Slab Dimensions
Need calculations for a different project size? Browse our complete engineering guides for popular slab footprints: