Your tanker just arrived and you have the scale receipt. You also know the target spread width and the controller setpoint in pounds per square yard. The next step is simple: calculate how far that load should carry so you can mark off the run before you start.

The Core Formula

Distance (feet) = 9 × L ÷ (W × R)

Where

  • L is the delivered load in pounds, taken from the scale receipt.
  • W is the spread width in feet.
  • R is the spread rate in pounds per square yard.
  • The constant 9 is a unit conversion factor that reconciles feet and square yards.

Why the 9 shows up

Your rate is in lb per square yard, but your measuring tape is in feet. One square yard equals 9 square feet, so multiplying by 9 aligns the units: solving L = R × area(yd²) for distance in feet with width in feet produces D = 9L ÷ (W × R).

Worked Example

Given: 52,000 lb load, 8 ft width, 68 lb/yd² target rate
Distance: D = 9 × 52,000 ÷ (8 × 68) = 860 ft.

Paint or flag a continuous 860 ft run at 8 ft wide and that tanker should finish right at your mark if the controller holds the target.

Planning One Long Pass or Many Short Passes

You can use the same math for road lanes, building pads, or parking lots.

One long pass

  1. Compute D from the formula.
  2. Measure that distance along the lane centerline and mark start and stop points.
  3. Spread to the stop mark.

Multiple short passes

If you plan to cover a wider strip with several side-by-side passes, keep everything in clean chunks of your spreader’s standard width. For an 8 ft spreader that is 8 ft, 16 ft, 24 ft, or 20 ft using two full-width passes plus one half-width pass.

  1. Decide how many passes you will make side by side right now
    For an 8 ft machine, two passes are 16 ft, three passes are 24 ft. If you need 20 ft, plan two full-width passes and one half-width pass.
  2. Use the distance formula with that combined width
    Distance (feet) = 9 × load (lb) ÷ [ width you plan to cover now (ft) × rate (lb/yd²) ]
  3. Mark one stop point at that distance
    Make each adjacent pass to the same stop mark. If you planned a half-width pass, run it to the same stop point.

Quick examples

  • 8 ft spreader, want 16 ft total
    Use width = 16 ft in the formula. Do two full-width passes to the same stop mark.
  • 8 ft spreader, want 20 ft total
    Use width = 20 ft in the formula. Do two full-width passes and one half-width pass to the same stop mark.
  • 8 ft spreader, want 24 ft total
    Use width = 24 ft in the formula. Do three full-width passes to the same stop mark.

Fast Workflow in the Field

  1. Read the receipt: record L in pounds.
  2. Confirm your plan width: W in feet.
  3. Use the controller setpoint: R in lb/yd².
  4. Compute D: 9L ÷ (W × R).
  5. Mark it: paint dots or use flags at the stop point for each pass.
  6. Spot check: when the tanker is empty, your measured distance should match D. If not, adjust calibration before the next load.

Sanity Checks You Can Do in Your Head

  • Doubling the width should halve the distance if everything else stays the same.
  • Increasing the rate means the distance gets shorter.
  • Bigger loads go farther in direct proportion.

Common Pitfalls and How to Avoid Them

  • Mixed units: keep width in feet and rate in lb/yd². The formula’s 9 handles the square yards to square feet conversion.
  • Wrong rate: verify the controller setpoint matches the spec rate before calculating.
  • Width drift: your driving centers should match the spreader width, which should match the spreading width set in the controller.
  • Rounding too early: carry an extra decimal in your calculator, then round your final distance to the nearest foot.

Another quick example

Given: 80,000 lb load, 12 ft width, 60 lb/yd² rate
Distance: D = 9 × 80,000 ÷ (12 × 60) = 720,000 ÷ 720 = 1,000 ft.

Summary

To mark off how far a tanker load should go at a known width and spread rate, use Distance (feet) = 9 × L ÷ (W × R). Grab the load from the scale ticket, confirm width and rate, compute the distance, and flag your stop points. It works for a single lane or any collection of shorter passes.