What size floor joist to span 10′, 12′, 15′, 16′, 18′, 20′, 24′ & 25 feet | what size floor joist to span 10 feet | what size floor joist to span 12 feet | what size floor joist to span 15 feet | What size floor joist to span 20 feet | what size floor joist to span 24 feet | what size floor joist to span 6 feet, 7 feet & 8 feet | floor joist spacing.

Typically 2×4, 2×6, 2×8, 2×10 and 2×12 different sizes of lumber used as floor joist in wooden frame structure, made of different species of wood (southern yellow pine & Douglas fir) and different grade such as grade – 1, grade – 2, grade – 3. Southern yellow pine is strongest species of wood that can span more distance compared to other species of wood. Grade 1 lumber have higher strength than other grade Lumber due to fewer knots.

**What is floor joist**

Floor joists can be define as several small beams. Floor joists are typically a horizontal structural member that runs across an open space of building on supporting wall or studs. Their function is similar as beams, except floor joists are supported by wall, foundations, or beams framing.

Floor joists usually run between walls or rafters to support a ceiling or floor. They transfer the dead load of the subfloor and floor finishes and live load of people, furniture and furnishings to beams, walls, headers, or foundation walls.

Floor joist is like the skeleton/ framing of a building that supports the load which the floor is built to bear. Joists are technically beams that typically spans relatively short distances compared to beams and are made of wood, steel, or engineered wood or lumber.

What size floor joist to span 10′, 12′, 15′, 16′, 18′, 20′, 24′ & 25 feet depending on different size of Lumber, species of wood, grade of wood, spacing between the joist, expected dead and live load of structure that coming to joist. The loading includes dead load of the weight of the frame structure & fixed weight and live load of People, furniture, appliances and a snow on the roof.

Not all the type of species of wood created equally strong and type of tree used to make joist affects the span allowed. Southern yellow pine is strongest species of wood that can span more distance compared to other species of wood. Grade 1 lumber have higher strength than other grade Lumber due to fewer knots.

Proper floor joist sizing is specified by the International Residential Code – the IRC. It outlines max span lengths for wood joists of all sizes – from 2×6 to 2×12 and greater. The code also identifies joist sizing and spans for various joist spacing – from 12” up to 24” apart.

**Floor joist size**

Size of floor joist range between 2×6to 2×12, but standard one is 2×8 (2 by 8). Others typical floor joist sizes are 2×6 (2-by-6), 2×8 (2-by-8), 2×10 (2-by-10), 2×12 (2-by-12) and even greater. A 2×6 size of floor joists, can allows joist max span lengths upto 12 feet and 2×12 size of floor joists, can allows joist max span length up to 25 feet.

Spacing between floor joist for different sizes are kept at 12 inches, 16 inches and 24 inches apart. The joist which are kept at lower spacing can allow longer distance to span as compared to joist spaced further apart. Standard spacing between floors joist is 16 inches.

**Floor joist spacing**

Most standard, floor joist spacing is 16 inches apart on center, but this can vary depending on building codes and the requirements of the structure. So, 12 inches, and 24 inches apart on center are also used. Floor joists help distribute the load of a structure. The joist which are kept at lower spacing can allow longer distance to span as compared to joist spaced further apart.

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**What size floor joist to span 10′, 12′, 15′, 16′, 18′, 20′, 24′ & 25 feet**

What size floor joist to span 10′, 12′, 15′, 16′, 18′, 20′, 24′ & 25 feet depending on different size of Lumber, species of wood, grade of wood, spacing between the joist, expected dead and live load of structure that coming to joist. The loading includes dead load of the weight of the frame structure & fixed weight and live load of People, furniture, appliances and a snow on the roof.

Floor joist span: A 2×4 (2-by-4) size of floor joist can be used to span span 6′, 7′ & 8 feet. A 2×6 (2-by-6) size of floor joist can be used to span span 10′, & 12 feet. A 2×8 (2-by-8) size of floor joist can be used to span span 15′, & 16 feet. A 2×10 (2-by-10) size of floor joist can be used to span span 18′, & 20 feet. A 2×12 (2-by-12) size of floor joist can be used to span span 24′, & 25 feet.

**What size floor joist to span 10 feet**

A 2×6 (2-by-6) size of floor joists, made of southern yellow pine, graded as #1, can be used to span 10 feet long when spaced 16 inches apart on O.C and live load of 30 Psf and dead load of 10 Psf.

You will need a 2×6 (2-by-6) size of floor joist, made of southern yellow pine, graded as #1, for 10 foot span when spaced 16 inches apart on O.C and live load of 30 Psf and dead load of 10 Psf.

A 2×6 (2-by-6) size of floor joists, made of southern yellow pine, graded as #1, can allow to maximum span up to 10 feet long when spaced 16 inches apart on O.C and live load of 30 Psf and dead load of 10 Psf.

**What size floor joist to span 12 feet**

A 2×6 (2-by-6) size of floor joists, made of southern yellow pine, graded as #1, can be used to span 12 feet long when spaced 12 inches apart on O.C and live load of 30 Psf and dead load of 10 Psf.

You will need a 2×6 (2-by-6) size of floor joist, made of southern yellow pine, graded as #1, for 12 foot span when spaced 12 inches apart on O.C and live load of 30 Psf and dead load of 10 Psf.

A 2×6 (2-by-6) size of floor joists, made of southern yellow pine, graded as #1, can allow to maximum span up to 12 feet long when spaced 12 inches apart on O.C and live load of 30 Psf and dead load of 10 Psf.

**What size floor joist to span 15 feet**

A 2×8 (2-by-8) size of floor joists, made of southern yellow pine, graded as #1, can be used to span 15 feet long when spaced 16 inches apart on O.C and live load of 30 Psf and dead load of 10 Psf.

You will need a 2×8 (2-by-8) size of floor joist, made of southern yellow pine, graded as #1, for 15 foot span when spaced 16 inches apart on O.C and live load of 30 Psf and dead load of 10 Psf.

A 2×8 (2-by-8) size of floor joists, made of southern yellow pine, graded as #1, can allow to maximum span up to 15 feet long when spaced 16 inches apart on O.C and live load of 30 Psf and dead load of 10 Psf.

**What size floor joist to span 16 feet**

A 2×8 (2-by-8) size of floor joists, made of southern yellow pine, graded as #1, can be used to span 16 feet long when spaced 16 inches apart on O.C and live load of 30 Psf and dead load of 10 Psf.

You will need a 2×8 (2-by-8) size of floor joist, made of southern yellow pine, graded as #1, for 16 foot span when spaced 16 inches apart on O.C and live load of 30 Psf and dead load of 10 Psf.

A 2×8 (2-by-8) size of floor joists, made of southern yellow pine, graded as #1, can allow to maximum span up to 16 feet long when spaced 16 inches apart on O.C and live load of 30 Psf and dead load of 10 Psf.

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**What size floor joist to span 18 feet**

A 2×10 (2-by-10) size of floor joists, made of southern yellow pine, graded as #1, can be used to span 18 feet long when spaced 16 inches apart on O.C and live load of 30 Psf and dead load of 10 Psf.

You will need a 2×10 (2-by-10) size of floor joist, made of southern yellow pine, graded as #1, for 18 foot span when spaced 16 inches apart on O.C and live load of 30 Psf and dead load of 10 Psf.

A 2×10 (2-by-10) size of floor joists, made of southern yellow pine, graded as #1, can allow to maximum span up to 18 feet long when spaced 16 inches apart on O.C and live load of 30 Psf and dead load of 10 Psf.

**What size floor joist to span 20 feet**

A 2×10 (2-by-10) size of floor joists, made of southern yellow pine, graded as #1, can be used to span 20 feet long when spaced 12 inches apart on O.C and live load of 30 Psf and dead load of 10 Psf.

You will need a 2×10 (2-by-10) size of floor joist, made of southern yellow pine, graded as #1, for 20 foot span when spaced 12 inches apart on O.C and live load of 30 Psf and dead load of 10 Psf.

A 2×10 (2-by-10) size of floor joists, made of southern yellow pine, graded as #1, can allow to maximum span up to 20 feet long when spaced 12 inches apart on O.C and live load of 30 Psf and dead load of 10 Psf.

**What size floor joist to span 24 feet**

A 2×12 (2-by-12) size of floor joists, made of southern yellow pine, graded as #1, can be used to span 24 feet long when spaced 16 inches apart on O.C and live load of 30 Psf and dead load of 10 Psf.

You will need a 2×12 (2-by-12) size of floor joist, made of southern yellow pine, graded as #1, for 24 foot span when spaced 16 inches apart on O.C and live load of 30 Psf and dead load of 10 Psf.

A 2×12 (2-by-12) size of floor joists, made of southern yellow pine, graded as #1, can allow to maximum span up to 24 feet long when spaced 16 inches apart on O.C and live load of 30 Psf and dead load of 10 Psf.

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**What size floor joist to span 25 feet**

A 2×12 (2-by-12) size of floor joists, made of southern yellow pine, graded as #1, can be used to span 25 feet long when spaced 12 inches apart on O.C and live load of 30 Psf and dead load of 10 Psf.

You will need a 2×12 (2-by-12) size of floor joist, made of southern yellow pine, graded as #1, for 25 foot span when spaced 12 inches apart on O.C and live load of 30 Psf and dead load of 10 Psf.

A 2×12 (2-by-12) size of floor joists, made of southern yellow pine, graded as #1, can allow to maximum span up to 25 feet long when spaced 12 inches apart on O.C and live load of 30 Psf and dead load of 10 Psf.

**What size floor joist to span 6′, 7′ & 8 feet**

A 2×4 (2-by-4) size of floor joists, made of southern yellow pine, graded as #1, can be used to span 6′, 7′, or 8 feet long when spaced 16 inches apart on O.C and live load of 30 Psf and dead load of 10 Psf.

You will need a 2×4 (2-by-4) size of floor joist, made of southern yellow pine, graded as #1, for 8 foot span when spaced 16 inches apart on O.C and live load of 30 Psf and dead load of 10 Psf.

A 2×4 (2-by-4) size of floor joists, made of southern yellow pine, graded as #1, can allow to maximum span up to 8 feet long when spaced 16 inches apart on O.C and live load of 30 Psf and dead load of 10 Psf.

**Conclusions:-**

A 2×6 (2-by-6) size of floor joist can be used to span span 10 feet. A 2×12 (2-by-12) to span 24 & 25 foot, 2×10 (2-by-10) up to 20 foot, 2×8 (2-by-8) up to 16 foot & 2×4 (2-by-4) up to 8 foot when spaced 16 inches apart.