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Benchwork Lumber Calculator
Quick answer
Open grid benchwork uses joists on 16 inch centres inside a perimeter frame. A 4 by 8 foot layout needs 7 joists totalling 28 feet, 16 feet of girder, two pairs of legs and one sheet of plywood or foam.
Benchwork is the part nobody photographs and the part that decides whether everything above it stays where you put it. It has one job: be flat, be rigid and stay that way as the humidity changes through the year.
The standard approach is open grid: a rectangular perimeter frame with joists across it on 16 inch centres, legs at the corners, and a top of plywood or extruded foam. Sixteen inch spacing is ordinary framing practice and it is what the sheet sizes assume, which is why it is worth following even though a model railroad carries almost no weight.
The load is not the reason for the structure. A layout weighs very little. The reason is stiffness: a top that flexes when you lean on it cracks plaster scenery and pulls solder joints off rail feeders, and a frame that twists as the seasons change puts kinks in trackwork that appear and disappear without explanation.
Benchwork lumber calculator
Framing lumber needed
| Part | Quantity | Length each | Total |
|---|
Roadbed and tools for the build
Top matches update when you change your numbers.
Woodland Scenics HO 2 foot Track-Bed Strips 12 Pack
$17.94Foam roadbed in pre-cut strips with the shoulder profile already there. Quieter than cork and it will not dry out and crumble the way cork can after some years.
Best for: HO roadbed that stays quiet
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Manton Cork Sheets Model Railroad Cork HO and O 12 by 36 by 1/4 inch 4-Pack
$55.72Cork sheet for yards and large paved areas, where you want a flat base at roadbed height rather than a shouldered profile.
Best for: yards and flat areas at roadbed height
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Woodland Scenics Foam Nails 2 inch 75 Pack
$9.24Holds foam roadbed and track down while the adhesive sets, then pulls out. Track pins driven into foam do nothing on their own.
Best for: holding track down while glue cures
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Woodland Scenics Foam Tack Glue 12 oz
$19.25Bonds foam without attacking it, which solvent adhesives do. This is what holds roadbed and foam risers down.
Best for: gluing foam roadbed and risers
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Excel Deluxe Model Railroad Tool Set
$67.57A knife handle, blades, files and a saw assembled specifically for model railroad work rather than a generic craft kit.
Best for: a complete modelling tool set from one brand
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HARDELL Digital Caliper 6 Inch with Large LCD
$22.99Measures in both inches and millimetres at the press of a button, which is exactly what scale modelling needs when standards are published in one and track in the other.
Best for: measuring and converting scale dimensions
Check price on AmazonLumber for common layout sizes
Open grid with joists on 16 inch centres and legs at roughly four foot intervals. Board feet here means linear feet of framing lumber, which is what you buy it by.
A 4 by 8 foot open grid layout needs 7 joists totalling 28 linear feet, 16 feet of girder and one sheet of plywood or foam.
| Layout size | Joists | Joist lumber | Girder lumber | Sheets | Total linear ft |
|---|---|---|---|---|---|
| 4 by 8 ft | 7 | 28 ft | 16 ft | 1 | 57.3 ft |
| 5 by 9 ft | 7 | 35 ft | 18 ft | 2 | 73 ft |
| 2 by 8 ft shelf | 7 | 14 ft | 16 ft | 1 | 43.3 ft |
| 30 by 80 in door | 6 | 15 ft | 13.3 ft | 1 | 41.7 ft |
| 6 by 10 ft | 8 | 48 ft | 20 ft | 2 | 88 ft |
A 4 by 8 sheet is 32 square feet, and cutting waste is real, so the sheet count rounds up. Buy the straightest lumber on the rack: a bowed joist transfers its bow to the track above it.
Plywood or foam on top?
Both work and they fail differently.
Plywood is rigid, takes screws anywhere, and supports a heavy structure or a lift-out section without complaint. It is also heavy, it transmits noise, and carving terrain into it is not practical, so scenery below track level means cutting holes with a jigsaw.
Extruded foam, usually one or two inches thick, is light, quiet, and can be carved below track level with a knife, which makes rivers and cuttings easy. It will not hold a screw, it needs support beneath it at closer intervals than plywood, and it must be glued rather than nailed because a driven fastener simply crushes it.
The common answer is both: a thin plywood deck for rigidity with foam on top for carving. That costs weight and height, and for a small layout foam alone over 16 inch joists is entirely adequate.
Height, and the decision people regret
Legs in this calculator are cut at 40 inches, which puts the railhead near chest height for a standing adult. That is deliberate, because it is roughly where most people end up after moving a layout at least once.
A low layout, around 30 inches, is easy to reach across and is the right choice if children will operate it or if you want to work sitting down. You view it from above, which reads as a model railroad seen from a helicopter.
A high layout, 48 inches and up, puts the train near eye level, which is the single biggest improvement to how a layout looks and costs nothing. It also makes the far side hard to reach, makes wiring underneath a comfortable job rather than a contortion, and rules out small children operating unaided.
The trade worth naming plainly: higher looks better and reaches worse. If the layout is against a wall and shallow, go high. If it is a wide island you must reach across, stay lower.
Frequently asked questions
What lumber should I use for model railroad benchwork?
Nominal 1 by 3 or 1 by 4 for joists and girders on a home layout is ample, because the structure needs stiffness rather than load capacity. Choose the straightest boards on the rack rather than the cheapest grade: a bowed joist transfers its bow into the plywood and then into the track above it, and that is very hard to correct later.
How far apart should benchwork joists be?
Sixteen inch centres is standard and is what the sheet sizes assume. You can go to 24 inches under plywood on a small layout without trouble. Under foam, closer is better, because foam is not stiff on its own and will sag between widely spaced supports over time, particularly if anything is sitting on it.
How high should a model railroad be?
Around 40 inches suits most adults standing, and is where many people settle after moving a layout once. Higher, up to about 50 inches, puts the train near eye level and looks considerably better, at the cost of reach. Lower, around 30 inches, is easier for children and for working seated. Higher looks better and reaches worse.
Is foam better than plywood for a layout top?
Neither is better, they fail differently. Foam is light, quiet and can be carved below track level with a knife, but holds no fasteners and needs closer support. Plywood is rigid, takes screws anywhere and supports heavy structures, but is heavy, noisy and awkward to cut terrain into. A thin plywood deck with foam on top combines both.
Do I need L-girder benchwork or is open grid enough?
Open grid is enough for almost every home layout and it is much simpler to build. L-girder comes into its own on large or irregularly shaped layouts, because risers can be screwed anywhere along the girder rather than only at a joist, which makes changing the track plan later far easier. For a rectangular table, open grid wins on simplicity.
How many sheets of plywood does a 4 by 8 layout need?
One, since a 4 by 8 sheet is exactly the footprint. Anything larger or an awkward shape should be worked out by area with waste allowed, because cutting loss is real and an odd shape wastes more. Buying one extra sheet is cheaper than a second trip, and the offcuts get used for risers and gussets.
Researched, not professional advice. This page is compiled from published manufacturer specifications, instruction manuals, published NMRA standards and recommended practices, and owner-review consensus, not hands-on testing. Figures described as a rule of thumb are hobby convention rather than a standard, and they are labelled that way wherever they appear. Always check a radius, a clearance or a grade against your own equipment before you cut wood or lay rail, because manufacturers vary and so does what your specific models will tolerate. Any permanent mains wiring in a layout room is work for a licensed electrician to your local code.