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Accurate estimation is the foundation of profitable delivery and predictable client costs. CharleOS uses a structured t-shirt sizing system combined with scoping best practices to estimate work consistently.

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Why Estimation Matters

Good estimation enables:

Profitability

Accurate estimates create margin when delivery is efficient

Client Trust

Realistic quotes build confidence and long-term relationships

Capacity Planning

Precise estimates enable better scheduling and resource allocation

Risk Management

Identifying complexity upfront prevents overruns

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The Estimation System

CharleOS combines two complementary approaches:
Relative estimation using standardized time rangesInstead of precise hours, work is sized using XS, S, M, L, XL, and XXL categories. Each size maps to a time range with a minimum, maximum, and average.Benefits:
  • Faster than precise hourly estimates
  • Accounts for uncertainty with ranges
  • Consistent across the team
  • Easy to explain to clients
Example:
  • “Homepage update” → M (3-6 hours)
  • Simple, clear, and feeds into billing formula

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How It Works Together

The estimation process follows a logical flow:
1

Understand the Requirement

Review the client’s request or requirement description. Ask clarifying questions if anything is ambiguous. Understand the desired outcome.
2

Scope the Work

Define what’s included:
  • What deliverables are expected?
  • What’s explicitly excluded?
  • Are there design and development components?
  • What dependencies exist?
Break large requirements into smaller, estimable pieces.
3

Apply T-shirt Sizes

For each scoped piece, select the appropriate t-shirt size:
  • Consider complexity, unknowns, and dependencies
  • Reference similar past work
  • Choose the size that fits the range
Remember: Each size includes core work PLUS QA/feedback buffer.
4

Validate the Estimate

Review the total estimate:
  • Does it feel reasonable compared to similar work?
  • Have you accounted for risks and complexity?
  • Is the scope clear enough to justify the estimate?
Adjust if needed before finalizing.

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Estimation in CharleOS

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Where Estimates are Used

When creating quotes, each requirement block is assigned a t-shirt size. The quote shows the time range to the client (e.g., “M: 3-6 hours”) and calculates the total estimated time.Requirements can have both design and development sizes for work with multiple components.
When quotes are converted to tasks, the t-shirt sizes carry over. Tasks inherit the estimate, which becomes the billing cap.Task-level estimates feed into:
  • Scheduling and capacity planning
  • Billing calculations (MIN/MAX formula)
  • Efficiency tracking (actual vs estimate)
Estimates are used to allocate capacity to the schedule. The system calculates how much time is needed and distributes it across available days.The 80/20 split (core work vs QA/feedback) helps allocate work to the right team members.

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Common Estimation Scenarios

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Scenario 1: Simple, Well-Defined Work

Example: “Update footer copyright year and add privacy link” Approach:
  • Work is clear and specific
  • No unknowns or dependencies
  • Quick change with minimal testing
  • Size: XS (0-30 minutes)

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Scenario 2: Moderate Complexity

Example: “Add product filtering by category on shop page” Approach:
  • Requires backend query changes and frontend UI
  • Existing patterns to follow
  • Standard testing required
  • Size: M (3-6 hours)

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Scenario 3: High Complexity

Example: “Build custom booking system with availability calendar” Approach:
  • Multiple components (calendar, booking form, admin)
  • Complex logic (availability, conflicts, notifications)
  • Extensive testing needed
  • Break it down:
    • Calendar UI: L (8-16 hours)
    • Booking logic: XL (24-40 hours)
    • Admin panel: M (3-6 hours)
    • Testing & polish: L (8-16 hours)
    • Total: 43-75 hours across multiple sizes
XXL sizes (40-120 hours) should be rare. If a requirement is XXL, consider breaking it into smaller deliverables to reduce risk and improve scheduling.

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Scenario 4: Unknown or Discovery Work

Example: “Investigate API integration options for [third-party service]” Approach:
  • Treat discovery as its own task
  • Size the discovery phase separately (usually S or M)
  • Estimate the implementation after discovery is complete
  • Discovery: S (1-2 hours)
  • Implementation: TBD (after discovery)

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Estimation Best Practices

If you’re torn between two sizes, choose the larger one. It’s better to deliver faster than expected (creating banked time) than to consistently overrun.Example: Feels like a large S or small M? → Choose M.
Smaller estimates are more accurate than large ones. Instead of one XL task, consider three M tasks. This also improves scheduling flexibility.Rule of thumb: If it’s XXL, try to split it.
Look at similar completed tasks:
  • How long did they actually take?
  • What was the estimated vs actual?
  • What unexpected issues arose?
Use history to calibrate your estimates.
Factors that increase complexity:
  • Working with unfamiliar tech
  • Client’s codebase is messy or undocumented
  • Multiple dependencies or stakeholders
  • High-risk changes (payment, auth, etc.)
Add buffer by sizing up when these factors are present.
T-shirt sizes include core work AND QA/feedback time. Don’t just estimate the happy path—account for:
  • Internal QA finding bugs
  • Client feedback requiring revisions
  • Multiple fix/review rounds
The 20% buffer is built in, but complex work may need a larger size.

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How Estimates Feed Billing

Estimates directly impact billing through the value-based formula: 
Billable = MIN(maximum, MAX(average, actual))
Example: M size (3-6 hours, average 4.5 hours)

Efficient Delivery

Actual: 3 hours
Billable: 4.5 hours (average)
Result: 1.5 hrs banked (profit)

On-Target Delivery

Actual: 5 hours
Billable: 5 hours (actual)
Result: No margin, but fair

Overrun

Actual: 7 hours
Billable: 6 hours (maximum)
Result: 1 hr overage (absorbed)
Why this matters:
  • Underestimating consistently creates chronic overruns, hurting profitability
  • Overestimating creates unrealistic client expectations and may lose deals
  • Accurate estimation balances risk and opportunity

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Tools and Resources

T-shirt Sizing Guide

Complete reference on size ranges, how to choose, and what’s included

Scoping Guide

Best practices for breaking down and defining work before estimating

Billing Model

How estimates feed into the value-based billing formula

Creating Quotes

Step-by-step guide to applying estimates in quotes