To figure out number of roof rafters you would need, measure the roof length or span between two end of wall in feet. Multiply the roof length in feet by 12 to convert in inches. Then divide it by spacing i.e 24″ or 16″ and add 1 in result and multiply by 2 for both side to get total number of rafters you needed.

To determine the number of rafters needed for a project, you’ll first need to consider factors such as the size of the roof, the spacing between rafters, and the pitch of the roof. Generally, rafters are spaced 16 or 24 inches apart.

- Measure Roof Span: Measure the total horizontal distance across the building to determine the roof span.
- Select Rafter Spacing: Decide on the spacing between rafters. Common spacings are 16 inches or 24 inches.
- Calculate Rafter Length: Use the Pythagorean theorem to calculate the rafter length based on the roof pitch and span.
- Determine Quantity: Divide the total roof span by the selected rafter spacing to determine the number of rafters needed.

## Formula to find number of rafters

The simple formula to find number of rafters are following: Roof rafters count = [【(roof length × 12)/spacing】 + 1】 2]. This equation will help you to figure how many rafters you needed. For example, if your roof span is 30 feet long and rafter spaced at 24″ oc, you will need at least 32 rafters for both sides. i.e (30×12)/24) +1 = 16 ×2 = 32 rafters.

**How far apart do rafters need to be?**

Typically, roof rafters need be spaced 24″ apart in the center. But it can be also spaced 12″ or 16″ apart. However, rafters are designed to the individual specification of a particular house. It also depends on local climatic conditions . For example, if you live in a hurricane-prone area, you can move the rafters need to be spaced 16″ in the center.

### How many rafters do I need for a 40 foot long roof?

In general, for a 40-foot long span roof in a residential building, you would need 42 rafters at 24″ oc, or 62 rafters at 16″ oc for both sides roof. Typically at 24″ oc, rafters count = [【(40 × 12)/24) + 1】 2] = 42 rafters, while at 16″ oc, rafters count = [【(40 × 12)/16) + 1】 2] = 62 rafters. So, you may require 42 to 62 rafters for a 40 foot roof span.

### How many rafters do i need for a 10 foot span

In general, for a 10-foot span, you would need 12 rafters at 24″ oc, or 18 rafters at 16″ oc for both sides roof. Typically at 24″ oc, rafters count = [【(10 × 12)/24) + 1】 2] = 12 rafters, while at 16″ oc, rafters count = [【(10 × 12)/16) + 1】 2] = 18 rafters. So, you may require 12 to 18 rafters for a 10 foot roof span.

### How many rafters do i need for a 12 foot span

In general, for a 12-foot span, you would need 14 rafters at 24″ oc, or 20 rafters at 16″ oc for both sides roof. Typically at 24″ oc, rafters count = [【(12 × 12)/24) + 1】 2] = 14 rafters, while at 16″ oc, rafters count = [【(12 × 12)/16) + 1】 2] = 20 rafters. So, you may require 14 to 20 rafters for a 12 foot roof span.

### How many rafters do i need for a 14 foot span

In general, for a 14-foot span, you would need 16 rafters at 24″ oc, or 24 rafters at 16″ oc for both sides roof. Typically at 24″ oc, rafters count = [【(14 × 12)/24) + 1】 2] = 16 rafters, while at 16″ oc, rafters count = [【(14 × 12)/16) + 1】 2] = 24 rafters. So, you may require 16 to 24 rafters for a 14 foot roof span.

### How many rafters do i need for a 15 foot span

In general, for a 15-foot span, you would need 18 rafters at 24″ oc, or 26 rafters at 16″ oc for both sides roof. Typically at 24″ oc, rafters count = [【(15 × 12)/24) + 1】 2] = 18 rafters, while at 16″ oc, rafters count = [【(15 × 12)/16) + 1】 2] = 26 rafters. So, you may require 18 to 26 rafters for a 15 foot roof span.

### How many rafters do i need for a 16 foot span

In general, for a 16-foot span, you would need 18 rafters at 24″ oc, or 26 rafters at 16″ oc for both sides roof. Typically at 24″ oc, rafters count = [【(16 × 12)/24) + 1】 2] = 18 rafters, while at 16″ oc, rafters count = [【(16 × 12)/16) + 1】 2] = 26 rafters. So, you may require 18 to 26 rafters for a 16 foot roof span.

### How many rafters do i need for a 18 foot span

In general, for a 18-foot span, you would need 20 rafters at 24″ oc, or 30 rafters at 16″ oc for both sides roof. Typically at 24″ oc, rafters count = [【(18 × 12)/24) + 1】 2] = 20 rafters, while at 16″ oc, rafters count = [【(18 × 12)/16) + 1】 2] = 30 rafters. So, you may require 20 to 30 rafters for a 18 foot roof span.

### How many rafters do i need for a 20 foot span

In general, for a 20-foot span, you would need 22 rafters at 24″ oc, or 32 rafters at 16″ oc for both sides roof. Typically at 24″ oc, rafters count = [【(20 × 12)/24) + 1】 2] = 22 rafters, while at 16″ oc, rafters count = [【(20 × 12)/16) + 1】 2] = 30 rafters. So, you may require 22 to 30 rafters for a 20 foot roof span.

### How many rafters do i need for a 24 foot span

In general, for a 24-foot span, you would need 26 rafters at 24″ oc, or 38 rafters at 16″ oc for both sides roof. Typically at 24″ oc, rafters count = [【(24 × 12)/24) + 1】 2] = 26 rafters, while at 16″ oc, rafters count = [【(24 × 12)/16) + 1】 2] = 38 rafters. So, you may require 26 to 38 rafters for a 24 foot roof span.

### How many rafters do I need for a 28 foot span

In general, for a 28-foot span, you would need 30 rafters at 24″ oc, or 44 rafters at 16″ oc for both sides roof. Typically at 24″ oc, rafters count = [【(28 × 12)/24) + 1】 2] = 30 rafters, while at 16″ oc, rafters count = [【(28 × 12)/16) + 1】 2] = 44 rafters. So, you may require 30 to 44 rafters for a 28 foot roof span.

### How many rafters do i need for a 26 foot span

In general, for a 26-foot span, you would need 28 rafters at 24″ oc, or 42 rafters at 16″ oc for both sides roof. Typically at 24″ oc, rafters count = [【(26 × 12)/24) + 1】 2] = 28 rafters, while at 16″ oc, rafters count = [【(26 × 12)/16) + 1】 2] = 42 rafters. So, you may require 28 to 42 rafters for a 26 foot roof span.

### How many rafters do i need for a 22 foot span

In general, for a 22-foot span, you would need 24 rafters at 24″ oc, or 36 rafters at 16″ oc for both sides roof. Typically at 24″ oc, rafters count = [【(22 × 12)/24) + 1】 2] = 24 rafters, while at 16″ oc, rafters count = [【(22 × 12)/16) + 1】 2] = 36 rafters. So, you may require 24 to 36 rafters for a 22 foot roof span.

### How many rafters do i need for a 30 foot span

In general, for a 30-foot span, you would need 32 rafters at 24″ oc, or 48 rafters at 16″ oc for both sides roof. Typically at 24″ oc, rafters count = [【(30 × 12)/24) + 1】 2] = 32 rafters, while at 16″ oc, rafters count = [【(30 × 12)/16) + 1】 2] = 48 rafters. So, you may require 32 to 48 rafters for a 30 foot roof span.

### How many rafters do i need for a 36 foot span

In general, for a 36-foot span, you would need 38 rafters at 24″ oc, or 56 rafters at 16″ oc for both sides roof. Typically at 24″ oc, rafters count = [【(36 × 12)/24) + 1】 2] = 38 rafters, while at 16″ oc, rafters count = [【(36 × 12)/16) + 1】 2] = 56 rafters. So, you may require 38 to 56 rafters for a 36 foot roof span.

#### Conclusions

To **figure out number of roof rafters** you would need, use the simple formula to **find number of rafters** are following: Roof rafters count = [【(roof length × 12)/spacing】 + 1】 2].