THE MOTHER OF CALCULATORS
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PlanCalc is the ultimate toolkit for Site Development and Engineering. This professional suite bridges the gap between design and math with precise tools for grading, drainage, and planting.

Scale Converter
Convert plan dimensions to real-world units. Supports 1:50, 1:100, 1:250 & more.
Side Slope
Calculate contour line angles and setbacks for paths with cross-slope.
Slope Grading
Calculate percentages, angles, and terrain functions (Access vs. Stabilization).
ADA Ramps
Design accessible ramps with automatic landing calculations and handrail checks.
Stair Formula
Blondel Law (2R+T) calculator for comfortable Indoor & Outdoor stairs.
Manning Flow
Hydraulic flow rate (Q) for open channels, swales, and streams.
Surface Runoff
Rational Method (Q=CIA) for stormwater drainage estimation.
Plant Density
Estimate planting quantities for Square vs. Triangular grid spacing.
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Missing a specific calculation? Partner with us to develop the next generation of planning standards.
About PlanCalc
PlanCalc was developed by a practicing Landscape Architect to serve the daily needs of design professionals. While other software handles the drawing, this suite handles the engineering logic—ensuring your slopes are drainable, your ramps are compliant, and your planting quantities are accurate. Built for accuracy, speed, and professional confidence.
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Help Shape the Future of Site Engineering

PlanCalc is constantly evolving. We believe the best tools are built by those who use them daily in the field.

Whether you are a Architect, Engineer, or Project Manager—if you have a specific calculation methodology that would save you time, we want to hear it.

Let's collaborate to automate your workflow and expand the toolkit for the entire community.

— Orgad Markovich, Creator of PlanCalc
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Pos: 0.5
Contour Interval (0.2m Rise):-
Drawing Offset (Left Edge):-
Drawing Offset (Right Edge):-
Resultant Slope (True):-

Technical Notes

Grading & Cross Slope Analysis

Precise grading is essential for designing ADA compliant pathways and ensuring proper site drainage. This tool resolves the vector geometry between directional slope and cross fall.

  • Cross Slope: Critical for preventing standing water. Recommended range: 1.5% - 2.0%. Max 2% is the standard for accessible routes.
  • Longitudinal Slope: The gradient along the direction of travel.
  • Resultant Slope: The true vector sum of both slopes. This is the value that determines if a path is traversable or requires handrails.

Technical Notes

The Concept of Representative Fraction (RF)

Map scale is the ratio of a distance on the map to the corresponding distance on the ground.

Common Architectural Scales:

  • 1:50 - Detailed floor plans and sections.
  • 1:100 - Standard scale for building permits and general arrangements.
  • 1:250 - Site plans and landscape layouts.
  • 1:1250 - Urban planning and GIS maps.
Calculation Result
Enter 2 values & Calculate
0% - 3% | LEVEL & FURNISHABLEFully accessible; suitable for placing rigid furniture.
3% - 10% | LOUNGING & CIRCULATIONComfortable for walking and informal reclining.
10% - 18% | AMPHITHEATER SLOPEOptimal sightlines for ground seating.
18% - 33% | MAINTENANCE GRADIENTLimit for mechanical mowing.
33% - 58% | CRITICAL / GEO-STABILIZATIONNon-accessible; requires stabilization.

Technical Notes

Slope Stability & Grading Analysis

Slope analysis is crucial for ensuring proper site drainage, accessibility, and structural stability. This tool converts between the three common methods of measuring steepness:

  • Percentage (%) : The standard unit for roads and landscape grading. Formula: Rise / Run × 100.
  • Angle (°) : Commonly used in geotechnical engineering and friction analysis.
  • Ratio (1:X) : Used for earthworks (cut/fill) and retaining walls (e.g., a 1:3 slope is stable for most soils).

Key Thresholds: Maintain a minimum of 1.5% - 2.0% for drainage on paved surfaces to prevent ponding. Slopes greater than 5% are considered ramps and require handrails under ADA/Universal Design standards.

Run Length:-
Max Flight Allowed:-
Landings (Count):-
Total Length:-
Handrail:-

Technical Notes

Designing ADA Compliant Ramps

Ramp design is strictly regulated to ensure safety and accessibility for wheelchair users. Whether following ADA (USA) or IS 1918 (Israel), the geometry must prevent fatigue and tipping.

Critical Design Constraints:

  • Max Slope: The global standard is 8.33% (1:12). Steeper slopes are hazardous.
  • Cross Slope: Must not exceed 2.0% to ensure stability for wheelchair users.
  • Landings: A flat resting area (minimum 1.2m - 1.5m length) is required at the top, bottom, and whenever the vertical rise exceeds 75cm (30 inches).
  • Handrails: Mandatory on both sides for any ramp with a rise greater than 15cm. Handrails should extend 30cm horizontally beyond the top and bottom of the ramp run.
Target: 63 cm
Current Limit: 12
Steps:-
Formula Rule:-
Landings:-

Technical Notes

Ergonomics & The Blondel Law

The comfort and safety of a staircase are defined by the relationship between the Riser (R) and the Tread (T). Derived by François Blondel, the "Step Rule" ensures a natural walking cadence.

The Formula: 2R + T = 61cm - 63cm

Indoor vs. Outdoor Application:

  • Indoor: Space is often limited. A target of 61cm is common, with steeper risers (16-17.5cm).
  • Outdoor (Landscape): Steps should be shallower and treads longer to encourage a leisurely pace. A target of 63cm - 65cm is preferred. Common outdoor sizing: R=15cm, T=33cm.

Safety Note: Visual consistency is key. Risers and treads must not vary by more than 5mm within a single flight to prevent tripping hazards.

Flow Rate (Q):-

Technical Notes

Open Channel Hydraulics (Manning's Equation)

Calculate flow velocity and discharge (Q) for vegetated swales, drainage ditches, and channels using the standard Manning Formula.

Roughness Coefficient (n): Determines friction against flow.

  • n=0.013: Smooth concrete (high velocity, erosion risk).
  • n=0.035: Natural stone or earth with vegetation (slower flow, promotes infiltration).

Crucial for sizing channels to handle peak storm events without overflowing.

Runoff Volume (Q):-

Technical Notes

Stormwater Runoff (Rational Method)

The Rational Method (Q=CIA) is the standard Civil Engineering formula for estimating peak runoff rates for small drainage areas.

  • C (Runoff Coefficient): Represents surface impermeability.
    Forest/Park: ~0.2 | Pavement/Roofs: ~0.9.
  • I (Rainfall Intensity): Based on local IDF curves (e.g., "1 in 50 year storm event").
  • A (Area): The total catchment area draining to the point of design.
Total Plants:-
Density (p/m²):-

Technical Notes

Planting Density & Quantity Estimation

Professional estimator for Landscape Bills of Quantities (BOQ). Calculates precise plant counts for groundcovers, shrubs, and pavers based on spacing geometry.

  • Square Grid: Standard alignment for pavers or formal planting.
    Formula: Area / (Distance)².
  • Triangular (Hexagonal) Grid: The industry standard for groundcovers. Maximizes coverage and suppresses weeds. Requires ~15% more plants than square spacing.
    Formula: Area / (Distance² * 0.866).