Bench Seating Calculator

Bench inputs

Enter dimensions and cost assumptions. Use inches, centimeters, or millimeters. Results update after you press Calculate.

Units

All dimension fields use this unit.

Bench length

Overall end-to-end length.

Seat depth

Front-to-back sitting depth.

Seat height

Ground to seat top.

Backrest

Adds area and material estimates.

Backrest height

Used only when backrest is enabled.

Armrests

Reduces clear seating length.

Armrest width (each)

Used only when armrests are enabled.

Number of benches

Calculates totals for multiple builds.

Space per person

Uses the selected unit.

Custom space per person

Only used when space is Custom.

Lumber thickness (inches)

Thickness for area-based wood estimate.

Structure factor

Adds framing, legs, and waste allowance.

Finish sides

Two sides for full sealing outdoors.

Cost per board-foot

Use your local lumber price.

Hardware cost per bench

Fasteners, brackets, and pads.

Finish cost per ft²

Stain, paint, or sealer estimate.

Labor rate (per hour)

Optional for budgeting.

Hours per bench

Cutting, assembly, and finishing time.

Reset

Example data table

Scenario	Bench length	Seat depth	Seat height	Spacing	Benches	Capacity
Patio bench	72 in	18 in	18 in	18 in/person	1	4 people
Garden path rest	60 in	16 in	18 in	20 in/person	2	6 people
Firepit seating	84 in	18 in	19 in	22 in/person	3	9 people

Capacities round down to full seating spaces.

Formula used

Clear seating length: L_clear = L_total − 2 × W_arm (when armrests are included).
Capacity per bench: N = floor(L_clear / S_person).
Areas: A_seat = L_total × D_seat, A_back = L_total × H_back, A_arm = 2 × (W_arm × D_seat).
Board-feet estimate: BF = (A_total × T) / 144 × F_structure.
Finish area: A_finish = A_total × Sides, then convert to ft² by dividing by 144.
Total cost: Lumber + hardware + finish + labor.

How to use this calculator

Select your units, then enter bench length, depth, and height.
Enable backrest and armrests if your design includes them.
Choose a space-per-person value to estimate seating capacity.
Set lumber thickness and structure factor for material estimating.
Enter costs to create a budget, then press Calculate.
Use Download CSV or Download PDF to share results.

Seating Capacity Planning

Bench seating starts with clear usable length, not overall length. Subtract armrest width on both ends, then divide by your chosen spacing per person. Standard spacing is 18 inches, while 20 inches improves comfort with coats and tools. The calculator rounds down to whole seats, which helps avoid overcrowding on garden paths and patio edges. When planning layouts, keep walking clearance and planter access in mind for safety.

Comfort Dimensions for Outdoor Use

Seat height influences ease of standing, especially on uneven ground. Many outdoor benches work well around 17 to 19 inches high. Seat depth affects back support and circulation; 15 to 18 inches fits most adults. If you add a backrest, 12 to 18 inches of back height typically supports the lower back while keeping the profile light. For kids’ areas, consider slightly lower seats.

Material Estimation and Board-Foot Logic

To estimate lumber, the calculator converts seat, back, and arm areas into volume using thickness, then converts volume into board-feet by dividing by 144. A structure factor adds allowance for legs, framing, braces, and waste. For example, a factor of 1.35 covers typical joinery plus a modest cut-loss margin for garden-grade builds.

Finishing Area and Weather Protection

Finishing needs scale with surface area, not lumber volume. The calculator multiplies total panel area by one or two sides, then converts to square feet. Two-sided finishing is recommended for outdoor exposure because it reduces moisture cycling and checking. Use this estimate to plan stain, paint, or sealer quantities and to compare product coverage rates.

Budgeting and Procurement Notes

Cost outputs combine lumber, hardware, finish, and labor. Pricing per board-foot is useful when mixing species, while a per-bench hardware allowance captures fasteners, brackets, and feet. Labor hours can reflect on-site leveling and finishing coats. Add a small contingency for waste, site fixes, and extra finish coats. Exported results support shopping lists, client quotes, and consistent bench sets across gardens.

FAQs

1) What spacing per person should I use?

Use 18 inches for standard adult seating. Choose 20 inches for more comfort, bulky clothing, or arm movement. Use Custom when you want to match a site standard or a specific chair width.

2) Why does capacity round down?

Partial spaces usually feel cramped and cause crowding. Flooring the result gives a realistic count that fits without shoulder overlap. If you want a higher number, reduce spacing or increase clear seating length.

3) How accurate is the board-foot estimate?

It is a planning estimate based on panel areas, thickness, and a structure factor. Increase the factor for complex frames, curved parts, or high waste. Confirm with a cut list before final purchasing.

4) When should I finish both sides?

Finish both sides for outdoor benches exposed to rain, sprinklers, or ground moisture. Sealing all faces reduces swelling and checking. One-side finishing can work for covered areas when the underside stays dry.

5) What does the structure factor include?

It accounts for legs, stretchers, braces, joinery offcuts, and small errors. Typical values range from 1.20 to 1.60. Use a higher value for thicker legs, wide braces, or novice cutting.

6) Can I use centimeters or millimeters safely?

Yes. Select the unit first, then enter all dimensions consistently. The calculator converts internally to inches for formulas and converts back for display. Spacing per person also follows the selected unit.