The Girts for a Building calculator computes the number of rows of girts and their lengths for a building.
INSTRUCTIONS: Choose units and enter the following:
- (L) Length of Building
- (S) Span or Width of Building
- (H) Height of Walls (see diagram)
- (GS) Girt Spacing (default: 4')
- (GBL) Girt Board Length (default: 20')
Girts for Building (GB): The calculator returns the number of rows of girts, the length of each row, the total.
The Math / Science
Girts are horizontal boards, that are attached to the posts. Girts are used as the structural base for exterior siding and are similar to purlins on the roof but may be different lumber since they carry less of a vertical load. The Girts for a Building calculator uses the girt spacing to determine the number of rows from the bottom to the top. It then uses the Length and Width of the building to compute the length of the girt rows.
Purlins and Girts
Purlins are rows of boards nailed horizontally to a roof's frame to act as a base for surface materials such as a metal roof panels. Purlins are usually nailed but sometimes screwed to rafters or trusses and spaced in horizonal rows. The metal roofing panels are then screwed onto the purlins vertically forming the roof up to the ridge cap and down to the drip edge of the overhang.
Girts are like purlins and used on walls to be the base of metal panels for siding. 
Girts are horizontal boards nailed or screwed to vertical posts or studs, and they are used as the support structure to vertical wall panels such as metal siding. Girts are often 2x6 boards.
Pole Barn Calculator
The Pole Barn Calculator contains functions to compute the construction materials for a pole barn with concrete piers, a slab, wood framing, roof trusses for a normal gabled roof and metal panels and trim for the roof and siding.
- Gable Roof Metal: This estimates the materials needed for a metal roof for a simple gabled roof based on the roof dimensions.
- Purlins for a Roof: This computes the total number and length of purlins for a simple gable roof based on the ridge length of the roof, the roof pitch and the span of the roof.
- Trusses Needed for Roof: This computes the number of trusses needed for a roof based on the ridge length and spacing.
- Metal Siding for Gable Ends: This computes the metal siding materials (vertical panels) for a wall under a gable roof end based on the dimensions.
- Metal Siding for Gable End with Door: This computes the metal siding materials for a wall under a gable roof end based on the dimensions.
- Girts for a Building: This computes the number of rows of girts and their lengths for a building.
- Wall Beams for a Building: This computes the lengths beams for the outer wall of a building.
- Posts for a Building: This computes the number of vertical posts for a building based on dimensions and spacing.
- Rebar and Concrete in a Slab: This computes the total length and weight of rebar and the volume of concrete needed for a slab.
- Piers for a Building: This computes the number of piers for a building and the amount of concrete needed.
- Pole Barn Materials: This computes the top to bottom framing and roofing materials needed for a pole barn (see picture) based on a few dimension.
- Pole Barn Metal Roof and Siding Cost: This uses an estimated the linear feet of metal panels needed for a pole barn with a door way, and provides an estimated cost for the metal panels for the roof and siding based on a the dimension and cost per linear foot of panels.
- Corrugated Metal Paint or Coating Volume: This estimates the volume of paint or other coating (e.g., spray insulation) is needed for a corrugated surface.
IMPORTANT NOTE: Confirm all calculations with authoritative sources such as architectural drawings before risking health or wealth on the results of any calculator, and ALWAYS adhere to government approved building codes.