The Rebar Calculator contains equations and data used in working with reinforcement bars (rebar) in concrete slabs. The formulas calculate materials needed for rectangular, circular and irregular shaped slabs. 
(para español, HAGA CLIC AQUÍ) .
Reinforcement Bar (rebar) Functions
- Length of Rebar in Grid
- Weight of Rebar in Grid
- Rebar in a Wall
- Rebar in an Irregular Shaped Slab
- Rebar in a Circular Slab
- Rebar Lapping Length
- Rebar Cost Estimate
- Weight of any Length of Rebar
- Concrete Displaced by Rebar
Rebar Function Details
- Length of Rebar in Grid: The user enters the dimensions of the slab (Length and Width), the onCenter spacing of the rebar and the inset from the edge of the slab for the rebar grid. The user can also enter lapping factors: length of uncut rebar, rebar size and a lapping factor. The formula returns the total length of rebar needed to build such a grid (see diagram above).
Rebar in Irregular Shaped slab.
- Weight of Rebar in Grid: The user enters the dimensions of the slab as in the Length of Rebar in a Grid formula (above), and selects a size of rebar (see table). The formula calculates the total length needed for the grid and applies the weight measurement for the specified rebar size to provide the Total Weight of the Rebar Grid.
- Rebar in a Wall: This lets the user enter the dimensions of a wall and rebar specifications and computes the length and weight of rebar, the volume of concrete, and/or the surface area of the forms for a concrete wall.
- Rebar in an Irregular Slab: This function computes the length and/or weight of rebar in an irregular shaped slab based on the spacing and the rough area and perimeter of the slab.
- Rebar in a Circular Slab: This computes the length and/or weight of rebar in a circular slab based on the spacing and the radius of the slab.
- Rebar Lapping Length: This computes the length of rebar lapping based on the size of rebar and a lapping factor. The size is used to set the rebar diameter.
- Rebar Cost Estimate: This computes the estimated cost of rebar based on the total length of rebar, the length of the pieces (rebar sticks) and the per piece (stick) price. See Rebar Pricing below.
- Weight of a Length of Rebar: This lets the user enter any length and select a size of rebar. It then returns the weight of that length of rebar.
- Concrete Displaced by Rebar (NEW): This computes the net weight added to a slab by including rebar. It also computes the amount of concrete displaced by rebar in a slab. The users enters a length of rebar and its size. This computes the volume of concrete displaced and the net weight change since rebar is heavier than concrete.
Rebar Pricing
The following are price estimates of rebar products based on the current market price of steel and a reasonable markup from raw steel to retail rebar product.
| Current Rebar Price Estimate (2023-05-30) | ||
|---|---|---|
| Rebar Size | 20' Price | 40' Price |
| 3 | $5.76 USD | $9.96 USD |
| 4 | $9.99 USD | $17.94 USD |
| 5 | $14.84 USD | $27.46 USD |
| 6 | $21.4 USD | $39.96 USD |
| 8 | $37.31 USD | $68.59 USD |
Related Calculators
- Masonry Calculator
- Video Instructions see YouTube instruction video HERE.
- Spanish Rebar Calc: Calculadora de Barras de Refuerzo
Lapping
BN Products BNT-40X Rebar Tier
When the dimensions of your slab or wall exceed the length of a single piece of rebar, it is required to overlap and tie rebar pieces to create the added length. This is called Lapping, and the length of the overlapping rebar is the Lapping Length. There are a few considerations. First, the length of the lap is specified by a "Lapping Factor (LF)" which is often 40 times the diameter of the rebar. 60 is also a common factor, but the engineering specifications should always be applied. See these YouTube videos to better understand rebar lap:
The typical length of pre-cut rebar is 40' and 60' in the United States.
Forms
The Rebar in a Wall function also computes the size of the forms. Concrete forms are a vital part of construction. The Form Area of Concrete Wall function in this calculator helps compute the amount of plywood or OSB needed to construct the forms. It give you the choice of specifying whether you want to compute:
- One Side: This is just the face of one side of the form.
- Two Sides: This is the face of both sides of the form.
- Two Sides and Edges: This is the most common amount of plywood needed to build a form. It entirely encloses the volume to be poured. Plywood Forms for Concrete
History
The term rebar is short for reinforcement bars, and refers to bars of steel embedded in concrete to improve tensile strength.
Rebar Calc in Spanish
The Rebar Calculator is now available in Spanish. It has Spanish language descriptions, labels and diagrams and it also has default units in the metric system (SI). The lengths are in meters and centimeters, the areas are in square meters, the volumes are in cubic meters, and the weights are in kilograms and metric tons.