Floor Joist Calculator
Estimated Total Cost
$655 – $1,173
$2.92 – $5.23 per sq ft
Material
$319 – $501
Labor
$336 – $672
Joists Needed
13 joists
Board Feet
303 BF
Span Check: 2×10 at 16" OC supports up to 16 ft. Your 14 ft span is within the allowable range.
Disclaimer: Estimates are for budgeting purposes only. Actual costs vary by location, contractor, material availability, and project complexity. Always get professional quotes for exact pricing.
Floor Joist Cost Breakdown
| Joist Size | Cost / Linear Ft | Max Span (16" OC) | Typical Use |
|---|---|---|---|
| 2×6 | $0.90 – $1.50 | 10 ft | Short spans, closets |
| 2×8 | $1.25 – $2.00 | 13 ft | Bedrooms, small rooms |
| 2×10 | $1.75 – $2.75 | 16 ft | Standard residential |
| 2×12 | $2.50 – $4.00 | 20 ft | Large spans, heavy loads |
Average Project Costs by Room Size (16" OC)
| Project | Size (Span × Width) | Joist Size | Joists | Estimated Total |
|---|---|---|---|---|
| Small Room | 10 × 10 ft | 2×10 | 8 | $290 – $520 |
| Bedroom | 12 × 14 ft | 2×10 | 11 | $483 – $867 |
| Living Room | 16 × 20 ft | 2×10 | 16 | $928 – $1,664 |
| Room Addition | 20 × 24 ft | 2×12 | 19 | $1,670 – $2,960 |
How We Calculate
Our floor joist calculator estimates project costs using joist count and length as the base units. Material cost is calculated from total linear feet of lumber, while labor is applied per square foot of floor area.
How the math works: We divide the floor width by joist spacing (in inches) and add 1 to get the number of joists. Each joist runs the full span length, so total linear feet = joists × span. Material cost = total linear feet × cost per linear foot. Labor cost = floor area × labor rate per square foot. Board feet are calculated using nominal dimensions: (2 × depth × length) ÷ 12 per joist.
Joist Sizes Comparison
2×6 ($0.90–$1.50/LF) is suitable only for short spans under 10 ft, such as closets or small bathrooms. Rarely used as a primary floor joist in modern construction.
2×8 ($1.25–$2.00/LF) handles spans up to 13 ft at standard 16" OC spacing. Good for smaller rooms and second-floor bedrooms where the span is limited.
2×10 ($1.75–$2.75/LF) is the most common residential floor joist, spanning up to 16 ft at 16" OC. This is the standard choice for most new construction and remodeling projects.
2×12 ($2.50–$4.00/LF) is used for long spans up to 20 ft and heavy-load applications. Common in large room additions, garages, and open floor plans.
Spacing & Span Limits
Joist spacing directly affects load capacity and floor stiffness. Closer spacing (12" OC) allows longer spans and reduces floor bounce. Standard 16" OC is the residential default. 24" OC is code-minimum for light loads but may feel bouncy. Our max span values are based on the International Residential Code (IRC) for SPF #2 grade lumber with 40 psf live load and 10 psf dead load.
Additional Cost Factors
Our estimates cover joist lumber and installation labor but do not include rim boards/band joists ($2–$4/LF), joist hangers ($2–$5 each), bridging or blocking ($1–$3/LF), subfloor sheathing ($1–$2/sq ft), or structural hardware. For spans exceeding dimensional lumber limits, engineered lumber (LVL beams, I-joists) adds 50–100% to material costs.
Data Sources
Lumber pricing is compiled from Home Depot, Lowe's, and regional lumberyard quotes. Span tables follow the IRC (International Residential Code) for SPF #2 grade lumber. Labor rates reflect contractor estimates from HomeAdvisor, Angi, and RSMeans across multiple US regions.
Last updated: 2026-02-02
Frequently Asked Questions
How much do floor joists cost? +
Floor joist lumber costs $0.90–$4.00 per linear foot depending on size: 2×6 runs $0.90–$1.50/LF, 2×8 costs $1.25–$2.00/LF, 2×10 costs $1.75–$2.75/LF, and 2×12 costs $2.50–$4.00/LF. Installation labor adds $1.50–$3.00 per square foot of floor area. A typical bedroom floor (12×14 ft with 2×10 at 16" OC) costs $483–$867 total.
What size floor joist do I need? +
Joist size depends on span length and spacing. For standard 16" OC spacing with SPF #2 lumber: 2×6 handles up to 10 ft, 2×8 up to 13 ft, 2×10 up to 16 ft, and 2×12 up to 20 ft. These are based on 40 psf live load + 10 psf dead load per the IRC. For spans over 20 ft, use engineered lumber (LVL or I-joists).
How far can a 2×10 floor joist span? +
A 2×10 SPF #2 floor joist can span up to 16 ft at 16" OC (standard residential spacing), 19 ft at 12" OC, or 13 ft at 24" OC. These spans assume 40 psf live load and 10 psf dead load per the International Residential Code. Douglas Fir joists can span slightly farther than SPF.
What is the standard floor joist spacing? +
16 inches on center (OC) is the standard floor joist spacing for residential construction. 12" OC provides extra rigidity for heavy loads like tile floors or hot tubs. 24" OC is sometimes used for light loads in utility areas but may cause noticeable floor bounce. Always check local building codes for your specific application.
How many floor joists do I need? +
Divide the floor width (in inches) by the joist spacing and add 1. For example, a 20 ft wide floor at 16" OC needs: (20 × 12) ÷ 16 + 1 = 16 joists. This formula accounts for the first and last joist at each edge. Our calculator automatically computes this plus total lumber cost.
Can I sister floor joists instead of replacing them? +
Yes, sistering — bolting a new joist alongside a damaged or undersized one — is common for repairs and reinforcement. It costs less than full replacement since you avoid removing the subfloor. Sister joists should span the full length and be the same size or larger than the original. Use structural screws or through-bolts, not nails.
Do I need a permit for floor joist work? +
Yes, floor joist installation and replacement is structural work that typically requires a building permit in most jurisdictions. New construction always requires permits and inspections. Repairs like sistering a few joists may not require a permit in some areas, but check with your local building department to be sure.
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