A sit and reach box is a simple five-sided wooden box with a flat top that extends past the foot plate, and you can build one in an afternoon with basic tools and about $20 in plywood. The standard box measures roughly 12 inches wide, 12 inches long at the base, and 12 inches tall, with a top plate that extends out to about 27 inches so you have room to reach forward and measure your flexibility.
Standard Dimensions
Commercial sit and reach boxes follow the original Wells and Dillon design. The Lafayette Instrument version, widely used in fitness labs, has a base that is 18 inches long, 12 inches wide, and about 12 inches tall (some models go up to 13.75 inches), with a top plate that extends to 27.5 inches long. For a DIY version, you can simplify this. The critical measurements are the height of the foot plate (about 12 inches), the width (12 inches), and a top surface long enough to mount a ruler or tape measure that extends well past where your feet rest.
If you’re building this for a school fitness test or personal training, a 12-inch cube with a top that overhangs by 12 to 15 inches on the reaching side works perfectly. That overhang is where the ruler goes and where your hands travel during the test.
Materials You’ll Need
Half-inch or three-quarter-inch plywood is the best choice. It’s sturdy enough to press your feet against without flexing and cheap enough that the whole project costs very little. Here’s what to gather:
- Two side panels: 12 inches wide by 12 inches tall
- One bottom panel: 12 inches by 12 inches
- One foot plate: 12 inches wide by 12 inches tall (this is the vertical board your feet push against)
- One top plate: 12 inches wide by 26 to 28 inches long
- Wood glue
- Wood screws: 1.25-inch screws work well for three-quarter-inch plywood
- A ruler, yardstick, or tape measure
- Sandpaper: 120-grit for shaping, 220-grit for finishing
You’ll also need a drill, a saw (a circular saw or table saw for straight cuts), and a carpenter’s square to keep everything aligned.
Cutting and Assembly
Start by cutting all five pieces. The box is open on the back (the side opposite the foot plate), which is where the person sits on the floor and extends their legs into it. Think of it as a rectangular tunnel: the foot plate is the far wall, the bottom keeps the box off the ground, the two sides hold everything together, and the top extends past the foot plate toward the person being tested.
Assemble the base first. Attach the two side panels to the bottom panel using wood glue and screws every 3 to 4 inches along each joint. Pre-drill your holes to prevent the plywood from splitting. Then attach the foot plate across the front, flush with the edges of the side panels and the bottom. This creates a three-sided box with an open back and an open top.
Next, attach the top plate. Position it so the front edge is flush with the foot plate and the rest extends backward, past the open end of the box. This overhang is essential. It’s the reaching surface. Screw the top plate into the tops of the side panels and into the top edge of the foot plate. The top should be perfectly flat and stable enough to support someone pressing their hands down on it.
Finishing for Bare Feet and Hands
Since this box gets used with shoes off, splinters are a real concern. Sand every surface with 120-grit sandpaper first to remove rough spots and soften edges, then go over the foot plate and top surface with 220-grit for a smooth finish. Pay extra attention to the top edge of the foot plate, where the soles of feet press during testing.
Applying a coat of polyurethane sealant or an oil-based wood finish prevents the plywood from checking and splintering over time. This is especially important if the box will be stored in a gym or garage where temperature and humidity change. Let the finish cure fully (usually 24 hours) before using the box.
Adding the Measuring Scale
This is the step that determines whether your box gives accurate, meaningful scores. You have two common options: attach a yardstick to the top surface, or use a retractable tape measure mounted in a channel.
For the simplest approach, glue or tape a yardstick along the center of the top plate so it runs from the foot plate end toward the overhang. The critical detail is where you position the zero point. In the YMCA/ACSM protocol, the 15-inch mark (or 38 cm) on the ruler aligns with the edge of the foot plate, the exact spot where the bottoms of your feet rest. This means if you can only reach your toes, you score 15 inches. Reaching past your toes increases the number; falling short decreases it.
Some testing protocols use a metric scale with the zero point set at 23 cm or 26 cm at the foot line. If you’re using the box for a specific fitness test at a school or organization, check which standard they follow. The difference between 23 cm and 26 cm norms is just 3 cm, but it changes how you interpret results against published scoring tables. When in doubt, use the 26 cm (or 15-inch) setup, since that’s what most ACSM-based norms reference.
How to Use It Correctly
Sit on the floor with your legs extended straight through the open back of the box. Your feet should press flat against the foot plate, about hip-width apart (roughly 12 inches between your heels). Remove your shoes. Keep your knees straight but not locked or forced down.
Stack your hands with palms facing down, one on top of the other. Exhale slowly and reach forward along the top of the box three times, pushing the ruler marker or sliding your fingertips along the yardstick. Record the farthest point you reach on your best attempt. Reaching past your toes is generally a positive result for hamstring and lower back flexibility.
Optional Upgrades
If you want a sliding indicator like the commercial versions, you can make one from a small block of wood that sits in a shallow channel routed into the top plate. Push the block forward with your fingertips, and it stays in place when you pull your hands back, making it easier to read your score without a partner watching the ruler.
For portability, you can use small hinges and a latch to make the box collapsible, or simply build it from lighter, thinner plywood (half-inch instead of three-quarter). Adding rubber feet to the bottom prevents the box from sliding on smooth gym floors. A strip of adhesive-backed rubber on the foot plate gives a more comfortable surface for bare feet and keeps the box from shifting when you push against it.