Free Structural Grid Generator

Set out a structural grid in a minute: type the bay spacings, choose how the axes are labelled and get a dimensioned column grid with grid bubbles, ready for CAD. The built-in guide compares every bay with published typical spans for concrete floors, steel frames, mass timber and car parks, and flags the bays that fall outside the usual range. Everything is drawn in your browser and nothing you enter is uploaded.

How to use this structural grid generator

1. Type the bay spacings. On the Spacing tab, enter the spacings for each direction. Shorthand works: 3x8.1, 2x6 means three 8.1 m bays followed by two 6 m bays, and 2x8100mm is read as millimetres. In feet and inches write 3x30'-0", 20'-6".
2. Use the shortcuts. “Equal bays” sets a number of identical bays in one step. “Edit bays one by one” lets you change a single bay. Each direction takes up to 50 bays.
3. Label the axes. On the Labels tab, choose numbers or letters for each direction, the start label (such as 1, C or AA) and whether to count from the right or from the top. Letters skip I and O by default.
4. Set the symbols. On the Symbols tab, set the bubble diameter and position (both ends, top and left, or bottom and right), the grid line extension, the column section (square, rectangular, round or none), the bay and overall dimension chains, the north arrow and its angle, and a rotation for the whole grid.
5. Check the spans. Open the Guide tab and pick your structural system. Bays outside the typical range are listed with their axis labels and shown in orange on the drawing.
6. Edit on the drawing. Click or tap any axis to select it. You can then change the spacing before or after it, give it a custom label such as A.1, add an axis after it (which splits the next bay in half) or remove it (which merges the two bays either side).
7. Export. Download DXF for CAD, SVG or PNG for boards, CSV for coordinates, or save the grid as JSON. Print gives a one page sheet with the drawing, the bays and the guide notes.

How the grid is calculated

• Axis positions. Each axis sits at the running sum of the bay spacings, measured from the first grid intersection at (0, 0). With the default X bays of 3 x 8.1 m and 2 x 6 m, the axes fall at 0, 8.1, 16.2, 24.3, 30.3 and 36.3 m.
• Rotation. The grid is then rotated about that point by the angle you set.
• Bay check. Each bay is compared with the typical span range of the selected system. Bays below it are flagged as probably not economic, bays above it as longer than typical; where the source gives an extended span, bays up to it are reported as possible with a check on depth and deflection.
• Indicative depth. For the concrete systems the guide prints D = L / k, where L is the longest bay and k is the span to depth ratio the source gives for an interior span, for example L/36 for a reinforced flat slab with drop panels. It also notes when spans vary by more than 25 percent or panels exceed 2 to 1, which the CCAA charts do not assume.
• Car park check. With 2.4 m stalls, 0.3 m columns and 0.3 m clearance to the column face, the stalls that fit between columns are floor((spacing - 0.9 m) / 2.4) with a column between bays, or floor(spacing / 2.4) when the columns sit outside the stall rows. A clear span over two rows of 4.8 m stalls needs 15.60 m with a one-way aisle and 16.55 m with a two-way aisle.

With the defaults (X bays of 3 x 8.1 m and 2 x 6 m, Y bays of 3 x 7.5 m, RC flat slab with drop panels) every bay is inside the 6 to 9.5 m range, the indicative slab depth for the 8.1 m bay is about 225 mm outside the drop panels, and the guide adds a note that the spans vary by more than 25 percent. Typical ranges are for early planning only. Spans depend on loads, fire, vibration and local codes; confirm with a structural engineer.

Typical structural grid spacing by system

These are the ranges the guide uses. Every value comes from a published source; the tool does not estimate any of them.

The concrete ranges and ratios come from the CCAA Guide to Long-span Concrete Floors (2nd edition, 2003). The steel figures come from the SteelConstruction.info page on multi-storey office buildings, which notes that 6 x 9 m and 7.5 x 12 m column grids are commonly used, with facade columns typically 6 to 8 m apart. The mass timber ranges come from WoodWorks’ guidance on efficient structural grids, and the car park values from the IStructE tables as reproduced by SteelConstruction.info.

For an RC band beam, a bay of 7 to 8 m is reported as being at the lower end of the economic range rather than flagged as a warning, because CCAA gives the minimum economical span for a band beam as about 7 to 8 m; reinforced bands should not normally exceed 12 m, and longer ones are usually prestressed. There is no row for a conventional RC beam and slab, because the sources give only depth ratios for it; use the band beam row instead.

How to label grid lines

The common convention, and the default here, is numbers in one direction and letters in the other: X axes run 1, 2, 3 from left to right and Y axes A, B, C. The letters I and O are skipped because they are easily read as 1 and 0 on drawings and on site. To count from the other end, tick “Count from the right” or “Count from the top”.

Intermediate axes are where grids usually get messy. When a column line has to be added between B and C late in the design, select axis B, press “Add axis after” and give the new axis a custom label such as B.1 or 2a. Custom labels take up to eight characters, and the tool warns if one is used twice. Once drawings are issued, keep labels stable: renumbering after an inserted axis breaks every reference in the set and the engineer’s model.

Planning a car park or mixed use grid

Select “Car park, 90 degree stalls” in the guide and every bay gets a stall count. A column spacing of 8.1 m holds three 2.4 m stalls with a column between bays, and 7.2 m holds three when the columns sit outside the stall rows. In the other direction, a clear span of 15.60 m covers two rows of stalls and a one-way aisle, and 16.55 m a two-way aisle.

This is where office and parking grids clash. Offices want a grid set by the facade module, parking wants multiples of 2.4 m stalls. If the office grid gives bays that hold two and a half cars, either the grid changes or a transfer structure picks up the columns, a decision that is cheaper now than after the plans are drawn.

For a surface lot, or to count the stalls on a whole site at different angles, use the parking layout generator.

Exporting the grid to AutoCAD, Revit or Rhino

The DXF export uses the plain R12 ASCII format, the most widely readable DXF version. Grid lines sit on a GRID layer with a CENTER line type, columns on COLUMN, dimension lines on DIM and labels on TEXT, while the bubble circles stay continuous. Choose the DXF units before you export (millimetres, metres, inches or feet), so the file comes in at the right size without scaling. Dimensions are lines and text, the most portable option in R12.

In AutoCAD, insert the file as an external reference or a block on its own layer and trace your walls over it. In Revit, link the DXF into a plan view and use it to place grids. Rhino opens the file directly. To match your office layer names, see our article on CAD layer standards.

SVG keeps the drawing sharp at any size, and PNG is exported 2400 px wide. On large grids, bubbles and text in SVG, PNG and Print are enlarged so labels stay readable; axes and columns never move, and the DXF stays at full size. The CSV lists every axis with its label, offset and end coordinates, and every intersection.

Limits of the tool

• Grids are rectangular and orthogonal. They can be rotated, but radial and skewed grids are not supported.
• It does not design the structure. The guide compares bays with typical spans and gives an indicative depth for scheme sizing; member sizes, loads, fire and vibration need a structural engineer.
• Most sources reflect UK, Australian and US practice.
• There is no area take-off or scale tool; it sets out the grid and nothing else.

For the wider background on grid types and how they shape a plan, see our article on structural grid systems in architecture.

Frequently asked questions

What is a typical structural grid spacing for an office?

Composite steel offices commonly use 6 x 9 m or 7.5 x 12 m grids, and long-span cellular beams reach 10 to 15 m, according to SteelConstruction.info.

What span can a reinforced concrete flat slab reach?

The CCAA guide puts the economical span of a reinforced flat slab with drop panels at about 9.5 m and of a post-tensioned flat slab at about 12 m. Flat plates without drop panels are economical at about 6 to 8 m reinforced and 8 to 12 m post-tensioned.

What column spacing works for a car park?

Three 2.4 m stalls need 7.2 m between column centres when the columns sit outside the stall rows, or 8.1 m with a column between bays. A clear span over two stall rows and the aisle needs 15.60 m with a one-way aisle and 16.55 m with a two-way aisle.

Why do grid labels skip I and O?

They are easily mistaken for the numbers 1 and 0 on drawings and on site.

Can I open the export in AutoCAD?

Yes. The DXF is a plain R12 ASCII file with GRID, COLUMN, DIM and TEXT layers, in the units you choose. Exported files were checked with the independent ezdxf library.

Does the tool design the structure?

No. It sets out the grid and compares the bays with published typical spans. Member sizes and the final grid must come from a structural engineer.