Question 1

What rebar size should I use?

Accepted Answer

#3 (3/8 inch) rebar is suitable for thin slabs under 4 inches. #4 (1/2 inch) is standard for most residential slabs 4-6 inches thick, including patios and sidewalks. #5 (5/8 inch) is recommended for heavier loads, thicker slabs, or commercial applications. When in doubt, consult local building codes or a structural engineer.

Question 2

What is standard rebar spacing?

Accepted Answer

12 inches on center is the most common spacing for residential concrete slabs. For driveways with heavy vehicles or equipment pads, use 6 inch spacing for increased strength. For lighter applications like patios and walkways, 18 inch spacing is often sufficient. The calculator lets you set X and Y spacing independently for different requirements.

Question 3

Do I need rebar in both directions?

Accepted Answer

Yes, rebar should form a grid pattern with bars running in both directions (perpendicular to each other). Single-direction rebar only resists cracking in one direction. A proper grid provides crack resistance in all directions and is required by most building codes for structural slabs.

Question 4

How much overlap for splicing rebar?

Accepted Answer

Minimum lap splice length is typically 24 inches (40 times the bar diameter) for #4 and #5 rebar. For #3 rebar, 18 inches is common. The calculator includes a 10% default waste factor that accounts for overlaps, cuts, and unusable pieces. Always tie splices with wire ties at staggered locations.

Question 5

Can I use welded wire mesh instead of rebar?

Accepted Answer

Welded wire mesh (WWM) is acceptable for thin slabs (3-4 inches) with light loads, such as interior floors and light-duty patios. Rebar is preferred for driveways, structural slabs, exterior applications in freeze-thaw climates, and slabs thicker than 4 inches. Rebar provides better crack control and structural integrity.

Question 6

How do I calculate rebar weight from linear feet?

Accepted Answer

Multiply total linear feet by the weight per foot for your bar size: #3 = 0.376 lb/ft, #4 = 0.668 lb/ft, #5 = 1.043 lb/ft, #6 = 1.502 lb/ft. For example, 200 linear feet of #4 rebar weighs about 134 lbs (200 x 0.668). The calculator handles this automatically.

Size	Diameter	Weight/ft	Typical Use
#3	3/8"	0.376 lb	Thin slabs, temperature steel
#4	1/2"	0.668 lb	Residential slabs, driveways
#5	5/8"	1.043 lb	Heavy loads, commercial
#6	3/4"	1.502 lb	Structural, heavy commercial
#7	7/8"	2.044 lb	Foundations, columns
#8	1"	2.670 lb	Heavy structural

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