Planter Sizes: Box, Window Box and Raised Bed Dimensions

Rectangular planter box sizes

Rectangular planters are listed as length × width × height, usually outside dimensions. The soil volumes below are for the inside of a box with thin walls; subtract the wall thickness if yours is wood or concrete.

To work out any box: length × width × depth in inches, divided by 231 for US gallons or by 1,728 for cubic feet. In metric, cm × cm × cm ÷ 1,000 gives liters.

Window box sizes

A window box looks right when it matches the width of the window including its trim, or runs up to a few inches longer. Shorter boxes look skimpy; much longer ones look like a shelf.

• Depth and width: 8 in (20 cm) inside is the practical minimum. Boxes 6 in deep dry out within a day in summer sun.
• Liners: plastic or coir liners are sold to fit 24, 30, 36 and 48 in boxes. Buy the box first, then the liner, measuring the inside.
• Brackets: a 36 × 8 × 8 in box full of wet mix weighs about 60 to 90 lb (27 to 41 kg). Use at least two brackets fixed into studs or masonry, and three for boxes over 36 in.

Large planters by gallon size

Large planters are often sold by capacity. For a cube, the inside edge is the cube root of the volume; for planning, here is what each common capacity measures.

Round pots by diameter, nursery "gallon" containers and metric liter pots are covered in the flower pot size chart.

How deep a planter needs to be

Root depth is the dimension that decides what grows well. University extension services give similar minimums for container vegetables:

Width matters too. Allow about 12 in (30 cm) of soil surface per tomato or pepper plant and 4 to 6 in per lettuce or herb plant.

Raised bed planter sizes

A raised bed is a large, bottomless planter. The standard width is 4 ft, because most people can reach 2 ft into a bed from each side without stepping on the soil. Beds against a wall should be no more than 2 to 3 ft wide.

Divide cubic feet by 27 for cubic yards: a 4 × 8 ft bed 11.25 in deep needs 1.1 cu yd. Soil settles by 10 to 20% in the first season, so order a little extra.

Board heights for raised beds

Nominal lumber is smaller than its name. A "2 × 6" is 5.5 in (14 cm) wide, a 2 × 8 is 7.25 in, a 2 × 10 is 9.25 in and a 2 × 12 is 11.25 in (28.6 cm). Two stacked 2 × 6 boards make an 11 in bed. Inside dimensions also lose 3 in (two 1.5 in board thicknesses) in each direction unless you cut the boards to fit around the outside. The lumber sizes chart lists every nominal size.

• Paths between beds: 18 to 24 in (46 to 61 cm) to walk and kneel; 36 in (91 cm) if a wheelbarrow or wheelchair needs to pass.
• Waist-high beds: 24 to 36 in (61 to 91 cm) tall for gardening without bending. Planters on legs are usually 30 to 32 in to the rim with 8 to 12 in of soil.

Interior vs exterior dimensions

Walls take more room than they appear to. Subtract twice the wall thickness from each outside dimension to get the inside size:

• Plastic and resin: about 0.25 in (6 mm) walls; inside size is about 0.5 in less.
• Wood boards: 0.75 in (1× boards) or 1.5 in (2× boards); inside is 1.5 or 3 in less.
• Concrete, stone and thick fiberglass: 1 to 2 in; inside can be 4 in less.

Example: a 24 in cube with 1.5 in wood walls is 21 in inside and holds 5.4 cu ft, two-thirds of the 8 cu ft its outside size suggests. Self-watering planters lose a further 1 to 3 in of depth to the reservoir.

How heavy a filled planter is

Moist potting mix weighs roughly 40 to 50 lb per cubic foot (about 0.6 to 0.8 kg per liter); garden soil weighs about 75 to 100 lb per cubic foot. That adds up quickly on a deck or balcony.

A planter is also only as useful as its watering: a hose that reaches every bed is covered in the garden hose size guide. For placing planters on a deck or patio, see deck dimensions and patio furniture sizes; for storing tools and bagged soil, shed sizes.

Frequently asked questions