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Planning quantities depend on measured floorspace, proposed materials, and compliance constraints. Use the Area calculator for site and floor areas, the Construction Material calculator for delivery estimates, and the Building Regulations calculator for the technical standards that sit alongside planning permission.

The planning calculator covers the quantitative assessments required during the planning process — from calculating the Community Infrastructure Levy (CIL) charge on new development to determining car parking provision, cycle storage requirements, bin store capacity, permitted development thresholds, and planning obligations. These calculations appear at every stage of the planning process: pre-application discussions, planning applications, Section 106 negotiations, and post-approval discharge of conditions. Getting them right avoids planning application refusal, delayed discharge of conditions, and costly retrospective enforcement action.

UK planning policy is set at the national level through the National Planning Policy Framework (NPPF) but implemented locally through Local Development Frameworks (LDFs) and Local Plans. Many of the standards used in planning calculations — parking ratios, cycle storage requirements, affordable housing percentages — are set by individual Local Planning Authorities (LPAs) and vary significantly between areas. Always verify the applicable standards with your LPA before submitting a planning application.

The mode is selected automatically based on your topic: CIL charge, car parking, cycle storage, bin store, or permitted development threshold check.
For CIL: enter the chargeable floor area (gross internal area of new floorspace), the applicable CIL rate (£/m² from your LPA's CIL charging schedule), and any relief percentage applicable (social housing = 100%, self-build = 100%).
For parking: enter the gross internal area (GIA) or number of dwellings and the applicable parking ratio from your LPA's standards or the National Design Guide.
For permitted development: enter the original house footprint area and the proposed extension area — the calculator checks against standard PD thresholds (note: these are indicative only; prior approval may still be required).
For bin stores: enter the number of dwellings and the weekly waste volume — the calculator sizes the required storage space per current local authority recycling requirements.

Planning calculation formulas

CIL: Chargeable amount = Gross internal area (m²) × CIL rate (£/m²) × (1 − Relief%/100). CIL rates vary by LPA and by use class — some LPAs charge zero CIL; others charge £300+/m² for residential.

Car parking: Spaces required = GIA / Parking standard (where standard is m² GIA per space, from LPA's parking standards). Disabled bays = max(5%, 1 space) of total provision per BS 8300:2018.

Cycle storage: Spaces = Dwellings × Cycles per dwelling (typically 1 cycle space per bedroom, or 1 per studio; NPPF encourages higher provision for sustainable transport).

Bin store: Volume = Dwellings × Weekly waste volume × Storage period (weeks). Typical waste: 240L residual + 240L recycling per household per fortnight = 240L/week total.

Permitted development rear extension: max depth = 3m (attached) or 4m (detached), max height = 4m; prior approval required for 4–6m (attached) or 4–8m (detached) under the Prior Approval (larger home extension) procedure.

Reading your planning calculation

Key planning thresholds and standards

CIL relief: Social housing = 100% relief (mandatory); self-build = 100% (mandatory if eligible); charitable organisations = relief available (discretionary). Car parking standards (illustrative — always check LPA): residential = 1–2 spaces per dwelling (varies by location and public transport accessibility); office = 1 space per 30–50 m² NIA; retail = 1 space per 14 m² GEA (out-of-town) to zero (city centre). Permitted development (Class A — single storey rear extension): attached house = 3m depth without prior approval, up to 6m with prior approval (Article 4 directions may remove PD rights in conservation areas, Article 4 areas, or listed buildings). The 45-degree rule still applies in most LPAs — extensions must not overshadow neighbouring habitable rooms beyond a 45-degree line from the nearest window. All values are illustrative — planning decisions ultimately rest with the LPA.

Construction tips and best practices

Always check for Article 4 Directions in your area before assuming permitted development rights apply — conservation areas, HMO areas, and certain residential zones may have PD rights removed.
CIL is calculated on gross internal area, not net — even if you demolish existing floorspace, the CIL calculation starts with the total new-build GIA (with a deduction for demolished floorspace).
Pre-application discussions with the LPA before formal submission can identify parking, cycle, and refuse storage requirements early — avoiding redesign later is always cheaper than post-submission amendments.
Affordable housing thresholds vary by LPA: typically triggered by 10+ dwellings in England, with affordable housing percentage ranging from 10% to 35% of net new dwellings. Check your LPA's Local Plan viability assessment.
Fire escape widths are calculated per BS 9999 or BS EN 1838: minimum 1,050mm for routes serving more than 50 persons; 750mm for 1–50 persons. Travel distances to escape routes must comply with BS 9999 Table C.1.

Community Infrastructure Levy has raised over £800 million annually across England in recent years — with rates ranging from £0/m² to over £400/m² depending on location and development type.
The average planning application in England takes 10–13 weeks to determine (for minor applications) and 13–26 weeks for major applications — pre-application advice can reduce this by identifying issues early.
Approximately 10,000 retrospective planning applications are submitted annually in England — most of which relate to permitted development rights that were misunderstood or exceeded.
A standard residential car parking space requires approximately 13.5m² (5m × 2.5m bay, plus circulation) — for 50 spaces, this equals 675m² or more than two professional tennis courts.

Common mistakes to avoid

Assuming CIL applies at a fixed national rate — CIL rates are set locally and vary from £0 to £400+/m² for the same use class in different LPAs. Always download the current CIL charging schedule from the LPA's website.
Ignoring prior approval requirements for larger home extensions — a rear extension exceeding 3m (attached) or 4m (detached) requires prior approval notification even if it meets permitted development volume limits.
Forgetting that GIA includes existing retained floorspace in CIL calculations — if you convert an existing garage to habitable use and build a new rear extension, CIL applies to the new floorspace created, not just the extension.
Using national parking standards from the previous PPG13 (now withdrawn) instead of current LPA standards — many LPAs now have flexible or maximum (not minimum) parking standards for sustainable transport reasons.

Planning decisions in England and Wales are made by Local Planning Authorities under the Town and Country Planning Act 1990 and its secondary legislation. Community Infrastructure Levy is charged under the Community Infrastructure Levy Regulations 2010 (as amended). Permitted development rights are granted by the Town and Country Planning (General Permitted Development) (England) Order 2015. This calculator provides illustrative estimates based on common planning standards — it does not constitute planning advice, a planning application, or a pre-application consultation response. Always consult your Local Planning Authority and, for complex projects, a qualified Town Planner (MRTPI) before proceeding with development. Planning decisions are made on a case-by-case basis considering all material planning considerations.