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Yard Drainage Calculators for Runoff, Gravel, Storage & Slope

Use a focused calculator for one measurable question—roof runoff, storage, soil drain-down or slope—then switch to the full planner when sources and outlets interact.

Drainage planning workflow from water source to overflow
Use a calculator to answer one unknown at a time; use the full planner when those unknowns interact.
1Volume

How much water does this storm create?

2Grade

Can gravity move it along the proposed route?

3Soil

Can the proposed infiltration location accept water?

4Storage

How much can you hold before overflow begins?

Storm volume

Runoff volume

Rainfall × contributing area × explicit runoff coefficient, in US or metric units.

Roof storage

Rain barrel size

Compare roof runoff with barrel or cistern capacity and see captured water versus overflow.

Field soil

Infiltration test

Turn repeated water-level drop measurements into an observed in/hr or mm/hr field rate.

Storage

Dry-well storage screen

Translate target capture into water volume and gross stone-zone volume.

Material volume

French drain gravel

Estimate stone-zone volume, subtract pipe displacement and add an explicit ordering allowance.

Slope

Grade calculator

Convert measured horizontal run and elevation drop into percent grade.

Which calculation should you start with?

You know rainfall + contributing areaUse Runoff volume to quantify water volume first.
You are sizing rain barrels or a cisternUse Rain barrel size to compare available storage against roof runoff and overflow.
You are considering buried storageMeasure the proposed location with the infiltration field test, then use the dry-well screen for storage volume.
You already know the trench dimensionsUse French drain gravel to estimate aggregate volume without turning material math into a design recommendation.
You measured elevation dropUse the grade calculator before assuming a gravity outlet is practical.
Several of those interactUse the full planner so storm, surfaces, sources and outlets stay in one workflow.
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