Decline Grade & Distance Calculator

Grade percent expresses the vertical rise as a percentage of the horizontal run: grade% = vertical ÷ horizontal × 100.

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Decline grade (%)

Vertical change / depth to develop

Enter your values and press Calculate to see results.

Before you rely on this: First-pass guide only. Verify safety-critical or regulated work against the relevant standards, your project requirements and a qualified professional.

How to use this calculator

Enter the decline grade as a percentage (e.g. 12.5 for a 1-in-8 ramp) — this is the vertical rise per 100 m of horizontal run.
Enter the vertical change (depth to gain or lose) between the two points the decline connects, in metres.
Read off the horizontal run (plan distance), the incline travel length (actual drive metres to develop and drive along), and the equivalent 1:N ratio.

How it works

Grade percent expresses the vertical rise as a percentage of the horizontal run: grade% = vertical ÷ horizontal × 100. Rearranged for a known grade and vertical change, horizontal run = vertical ÷ (grade ÷ 100). The incline (travel) length — the actual distance driven along the sloping decline — is the hypotenuse: travel = √(run² + vertical²). The grade is also shown as a 1:N ratio where N = 100 ÷ grade%, so 12.5% is 1:8 and 14% is roughly 1:7.14.

This assumes a single straight decline at a constant grade — no horizontal curves, switchbacks or vertical transition curves, and no allowance for over-break or road build-up. Real declines add length through curves and typically sit between about 1:7 and 1:9 (roughly 11–14%) to suit truck haulage and rubber-tyred equipment. Use the travel length for development metres and schedule; use the run for plan layout. Guidance and estimate only — verify grade limits, geometry and ground conditions against your site's mine design and geotech.

Worked example

100 m of depth on a 1:8 (12.5%) decline. An underground access decline is designed at a 12.5% grade (a 1-in-8 ramp) and must gain 100 m of vertical depth to reach the next mining level. Enter grade = 12.5 and vertical change = 100. The tool returns a horizontal run of 800 m, an incline (travel) length of 806.23 m of drive to develop, and expresses the grade as 1:8. The travel length is what you multiply by your development advance cost/rate to estimate schedule and metres — always a little longer than the horizontal run because the drive slopes.

Common mistakes

Confusing the horizontal run with the travel length. On gentle grades they are close, but the drive you actually develop and haul along is the longer incline length (√(run² + vertical²)), which is what drives metres and cost.
Entering the grade as a ratio value (e.g. 8) instead of a percentage. A 1:8 decline is 12.5%, not 8% — convert with grade% = 100 ÷ N before entering.
Assuming a straight decline when the real design has curves or switchbacks. Those add length and are not captured here, so treat the output as a straight-line minimum.

Frequently asked questions

What is a typical grade for an underground decline?

Rubber-tyred haulage declines are commonly designed around 1:7 to 1:9, i.e. about 11% to 14%. Steeper grades shorten the drive but reduce truck payload and increase wear; flatter grades add length. Always follow your site's equipment and mine-design limits.

Why is the travel length longer than the horizontal run?

The decline slopes, so the distance driven along it is the hypotenuse of the run and the vertical change: travel = √(run² + vertical²). On a 12.5% grade gaining 100 m over an 800 m run, the travel length is 806.23 m.

How do I convert a percentage grade to a 1:N ratio?

Divide 100 by the grade percentage: N = 100 ÷ grade%. So 12.5% is 1:8, 14% is about 1:7.14, and 10% is 1:10. The tool shows this ratio automatically.

Does this account for curves, switchbacks or road build-up?

No. It models a single straight decline at a constant grade. Curves, switchbacks, vertical transition curves and floor build-up all add length, so treat the result as a straight-line minimum and confirm against the surveyed mine design.

Tip: Enter any known values to calculate the remaining results.

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